Chemistry test 2
1) The concept of a chemical bond is ________. A) how two or more atoms are held together B) how much energy it takes to remove an electron from a set of atoms C) the sharing of nucleons D) how two or more electrons reside in an orbital E) none of the above
a
15) The isotope Cesium-137, which has a half-life of 30 years, is a product of nuclear power plants. How long will it take for this isotope to decay to about one-sixteenth its original amount? A) 120 years B) 480 years C) 960 years D) 240 years
a
16) Which of the following elements has six valence electrons? A) O B) C C) Be D) B E) N
a
19) If the following generic atom were to undergo ionization, what would be the charge of most likely product? A) -3 B) +3 C) 8 D) -5 E) would probably not ionize
a
24) Given that the total number of atoms on our planet remains fairly constant, how is it ever possible to deplete a natural resource such as a metal? A) The problem is with the expense of collecting metal atoms that are uniformly dispersed. B) The problem remains that not everyone recycles as they should. C) The atoms donʹt leave our planet, which is why naturally occurring materials never really reach the point of depletion. D) Recycling only forestalls the inevitable depletion of metal resources.
a
25) Which of the following bonds would be the least polar? A) C-H B) C-Cl C) C-O D) C-F E) All are equally polar.
a
25) Which type of radiationalpha, beta, or gammaresults in the greatest change in atomic mass number? A) alpha radiation B) beta radiation C) gamma radiation D) They all result in the same change in atomic mass number.
a
26) Three kids sitting equally apart around a table are sharing jelly beans. One of the kids named Billy, however, tends only to take jelly beans and only rarely gives one away. If each jelly bean represents an electron, who ends up being slightly negative? Who ends up being slightly positive? A) Billy ends up being slightly negative, while the two other kids are both slightly positive. B) One of the two kids other than Billy ends up slightly positive, but Billy and the third kid will both end up slightly negative. C) Billy ends up being slightly positive, while the two other kids are both slightly negative. D) One of the two kids other than Billy ends up slightly negative, but Billy and the third kid will both end up slightly positive
a
3) Ordinary hydrogen is sometimes called a perfect fuel, because of its almost unlimited supply on Earth, and when it burns, harmless water is the product of the combustion. So why donʹt we abandon fission energy and fusion energy, not to mention fossil-fuel energy, and just use hydrogen? A) Hydrogen represents a viable solution for stored energy but not as a general energy source since obtaining the hydrogen from water requires more energy than is produced when you burn it. B) The political, economic, and corporate pressures being exerted to oppose abandoning the other energy sources are the only obstacles to moving to the use of hydrogen as the nationʹs primary energy source. C) The oil companies have lobbied the federal government to continue fossil fuel usage because it would mean huge profit losses for all the major oil conglomerates. D) The conversion of current energy consuming vehicles and other machinery to hydrogen, although simple, is going to be very costly to the consumer and difficult to legislate.
a
30) List the following bonds in order of increasing polarity: A) N-N < N-O < N-F < H-F B) N-N < N-O < H-F < N-F C) N-O < N-N < N-F < H-F D) H-F < N-F < N-O < N-N
a
32) Distinguish between a metal and a metal-containing compound. A) Only one of these contains ionic bonds. B) There is no distinction between the two. C) Only one of these occurs naturally. D) Only one of these contains covalent bonds.
a
33) Alpha and beta rays are deflected in opposite directions in a magnetic field because ________. A) they have opposite charges B) alpha particles contain nucleons and beta particles do not C) they spin in opposite directions D) all of the above
a
34) Which of the following best describes how a metal atom behaves within a bulk of metal? A) The metal ion shares its outermost electrons freely with its neighbors. B) The metal atom shares its electrons in a very directional manner. C) The metal atoms have limited interaction with neighboring atoms. D) The metal atom shares its electrons with only one other atom. E) none of the above
a
35) Which of the following does not describe ionic compounds? A) They have a tendency to melt easily. B) They are usually very ordered. C) They consist of positive and negative ions. D) They are held together by electrostatic attraction. E) none of the above
a
39) Which shows atoms in order of increasing electronegativity. A) Cs, Y, Ga, P, O, F B) Cs, F, Ga, O, P, Y C) F, O, Cs, Y, Ga, P
a
43) Why is carbon better than lead as a neutron absorber in nuclear reactors? A) Carbon slows down the neutrons making them more effective in stimulating the nuclear chain reaction. B) Lead slows down the neutrons making them less effective in stimulating the nuclear chain reaction. C) Carbon produces the high energy, high speed neutrons necessary for maintaining the nuclear chain reaction.
a
45) Which molecule is most polar? A) O=C=S B) S=C=S C) O=C=O D) These all have the same polarity.
a
46) If three samples have the half-lives listed below, which sample would remain radioactive the longest? A) a sample with a half-life of 20 million years B) a sample with a half-life of 20 hours C) a sample with a half-life of 20 years D) a sample with a half-life of 20 minutes E) none of the above
a
49) If an atom has 104 electrons, 157 neutrons, and 104 protons, what is its approximate atomic mass? A) The approximate atomic mass is 261. B) The approximate atomic mass is 365. C) The approximate atomic mass is 157. D) The approximate atomic mass is cannot be determined with the information given.
a
5) How many electrons are used to draw the electron-dot structure for calcium chloride, an ionic compound with the formula CaCl2? A) 16 B) 6 C) 8 D) 4
a
5) What is a hydrogen bond? A) a special type of dipole-dipole attraction involving hydrogen bound to a highly electronegative atom B) a special type of dipole-dipole attraction involving hydrogen bound to another hydrogen atom C) a special type of attraction involving any molecules that contain hydrogens D) a special type of dipole-dipole attraction involving hydrogen bound to any other atom E) none of the above
a
6) How many valence electrons does gallium (Ga, atomic no. = 31) have? A) 3 B) 6 C) 70 D) 31 E) 1
a
6) Under which of the following conditions would you expect the highest solubility of oxygen gas in water? A) low temperature and high O2 pressure above the solution B) high temperature and low O2 pressure above the solution C) The O2 solubility is independent of temperature and pressure. D) low temperature and low O2 pressure above the solution E) high temperature and high O2 pressure above the solution
a
7) How is the number of unpaired valence electrons in an atom related to the number of bonds that the atom can form? A) The number of unpaired valence electrons in an atom is the same as the number of bonds that the atom can form. B) The number of unpaired valence electrons in an atom is one-half the number of bonds that the atom can form. C) The number of unpaired valence electrons in an atom is twice the number of bonds that the atom can form. D) There is no defined relationship between the number of unpaired valence electrons and number of bonds that the atom can form.
a
8) When 218^ 84 Po emits a beta particle, it transforms into a new element. What are the atomic number and atomic mass of this new element? A) atomic number = 85; atomic mass = 218 B) atomic number = 82; atomic mass = 214 C) atomic number = 86; atomic mass = 214 D) atomic number = 84; atomic mass = 219
a
10) Which produces more energy: the fissioning of a single uranium nucleus or the fusing of a pair of deuterium nuclei into a helium-4 nucleus? A) Fusing a pair of deuterium nuclei produces more energy because there is a greater decrease in mass per nucleon. B) Fissioning a single uranium nucleus produces more energy because its change in mass is much greater than that of a pair of deuterium nuclei.
b
13) Why is it better to recycle metals than to mine more? A) Ores contain toxic elements. B) It takes far less energy to recycle. C) Mining is less expensive than recycling but not environmentally friendly. D) all of the above E) none of the above
b
14) How many substituents surround the sulfur atom in SF4? A) 1; one lone pair of electrons B) 5; four substituent fluorine atoms plus one lone pair of electrons C) 6; four substituent fluorine atoms plus two lone pairs of electrons D) 4; four substituent fluorine atoms
b
16) People who work around radioactivity wear film badges to monitor the amount of radiation that reaches their bodies. These badges consist of small pieces of photographic film enclosed in a light-proof wrapper. What kind of radiation do these devices monitor? A) Beta radiation B) Gamma radiation C) Alpha radiation D) all of the above
b
17) If carbon-14 is a beta emitter, what is the likely product of radioactive decay? A) oxygen-18 B) nitrogen-14 C) berrylium-10 D) carbon-12 E) none of the above
b
18) If uranium were to split into three segments of equal size instead of two, would more energy or less energy be released? A) Less energy would be released because of less mass per nucleon. B) More energy would be released because of more mass per nucleon. C) More energy would be released because of less mass per nucleon D) Less energy would be released because of more mass per nucleon.
b
26) If three samples have the half-lives listed below, which is the most radioactive? A) a sample with a half-life of 20 years B) a sample with a half-life of 20 minutes C) a sample with a half-life of 20 hours D) a sample with a half-life of 20 million years E) none of the above
b
31) How many nonbonding pairs of electrons are in the following molecule? HH A) 6 pairs B) 0 pairs C) 8 pairs D) 1 pair E) none of the above
b
32) Which of the beams is due to an energetic non-visible light wave? A) a B) b C) c D) all of the above E) none of the above
b
34) Radium-226 is a common isotope on Earth, but has a half-life of about 1600 years. Given that Earth is some 5 billions years old, why is there any radium at all? A) Radium-226 and Astatine-218 are converted back and forth via transmutation to one another at each of their respective half-life cycles. B) Radium-226 is a ʺdaughterʺ isotope and the result of the radioactive decay of uranium. C) Radium-226 and Radium-218 undergo a series of transmutation reactions of alpha and beta decay to repeatedly become one another approximately every 1600 years. D) Radium-226 is one of several self-transmutating isotopes of the elements of the periodic table and is able to replenish itself so that it is never depleted.
b
36) The neon atom tends NOT to lose any electrons because ________. A) that would result in a negative ion B) of its relatively strong effective nuclear charge C) its electrons are paired together within the same orbitals D) the ionization energy is so high
b
38) What is a rem? A) Rem is an ʹ80s rock group. B) A rem is a unit for measuring radiation exposure. C) Rem stands for Rapid Electron Motion. D) A rem is the number of radiation particles absorbed per second. E) A rem is the maximum exposure limit for occupational safety
b
40) Which of the following statements regarding a nucleon is true in regards to nuclear reactions? A) The number of nucleons changes in a nuclear reaction, therefore the mass changes. B) A nucleon inside a nucleus has a lower mass than a nucleon outside of the nucleus. C) A nucleon has a higher energy inside a nucleus, and releases it when it undergoes nuclear reactions. D) A nucleon is more stable outside the nucleus. E) A nucleonʹs mass is constant.
b
41) Phosphine is a covalent compound that contains phosphorus, P, and hydrogen, H. What is its chemical formula? A) PH B) PH3 C) H2P D) P2H3
b
42) Which of the following provides the minimum amount of protection you need to block the following form of radiation? beta A) T-shirt B) thick leather C) lead suit D) suntan lotion E) none of the above
b
42) Would ammonia, NH3, be more or less polar if its shape were triangular planar rather than triangular? A) more polar because of decreased symmetry of the molecule B) less polar because of the increased symmetry of the molecule C) The polarity would not be affected. D) more polar because of increased symmetry of the molecule
b
46) The number of nonbonding pairs in the water molecule is ________. A) one B) two C) three D) four
b
47) Which of the following statements best describes why a large nucleus is more likely to undergo radioactive decay? A) The proton-proton repulsion cannot overcome the nucleon attraction. B) The nuclear forces are not as strong as the repulsive electrical forces between nucleons. C) The nucleon-nucleon attraction is stronger than the proton-proton repulsion. D) The nuclear force between the nucleons are very strong and squeeze out other nucleons. E) All nuclei are equally likely to undergo radioactive decay
b
47) Why are metal ores so valuable? A) They hold many clues to Earthʹs natural history. B) Metals can be efficiently extracted from them. C) They tend to occur in scenic mountainous regions. D) They are sources of naturally occurring gold.
b
5) When 226^ 88 Ra decays by emitting an alpha particle, what is the atomic number of the resulting nucleus? What is the resulting atomic mass? A) atomic number = 87; atomic mass = 226 B) atomic number = 86; atomic mass = 222 C) atomic number = 86; atomic mass = 224 D) atomic number = 87; atomic mass = 224
b
50) What is a molecule? A) group of covalent compounds held together by ionic bonds B) a group of atoms that are held together by covalent bonds C) a group of atoms that are held together by ionic bonds D) pair of shared valence electrons E) pair of atoms sharing a set of valence electrons
b
50) Which of the following best describes an exothermic nuclear fission reaction? A) The energy released decreases with a greater loss of mass. B) The mass of the products is less than the mass of the reactants. C) The number of nucleons changes before and after the reaction. D) All of the above describe a fusion reaction. E) None of the above describe a fusion reaction.
b
10) If you mix a typical iodine ion (I, atomic no. = 53) with a typical barium ion (Ba, atomic no. = 56), what compound is formed? A) Ba56I53 B) Ba2I C) BaI2 D) Ba2I2 E) BaI
c
2) Just after an alpha particle leaves the nucleus, would you expect it to speed up? Why? A) No. As the alpha particle leaves the nucleus it is slowed by the constant attraction of the electrons surrounding the nucleus. B) No. Once the alpha particle leaves the nucleus it is slowed by the repulsion of the next closest atomʹs nucleus. C) Yes. Once the alpha particle leaves the nucleus it accelerates because of mutual electric repulsion with the nucleus from which it escaped. D) Yes. Once the alpha particle leaves the nucleus there are no more forces acting on it and it therefore accelerates.
c
2) Which of the following elements will most likely form an ion with a -2 charge? A) Cl B) Na C) S D) Ne E) Mg
c
20) A friend produces a Geiger counter to check the local background radiation. It ticks. Another friend, who normally fears most that which is understood least, makes an effort to keep away from the region of the Geiger counter and looks to you for advice. What do you say? A) The Geiger counter is emitting radiation. B) Run away as fast as you can! C) The Geiger counter is detecting naturally occurring radiation from your body. D) Wear heavy clothes.
c
21) The acronym VSEPR stands for ________. A) valentia sia electronus partium resonancius B) valence shell electron positive repulsion C) valence shell electron pair repulsion D) very significant electron pull resonance
c
21) What is the main technical difficulty in dealing with fusion reactions? A) The reactants are highly toxic and extremely radioactive. B) The mass of the reactants is less than the mass of the products. C) The amount of energy needed to overcome the electrical repulsion of the reactants is extremely high. D) It isnʹt possible to artificially generate the conditions needed for fusion. E) none of the above
c
22) Which of the following provides the minimum amount of protection you need to block the following form of radiation? alpha A) lead suit B) thick leather C) suntan lotion D) T-shirt E) none of the above
c
24) How is it possible for an element to decay ʺforward in the periodic tableʺ--that is, to decay to an element of higher atomic number? A) This only occurs during nuclear fusion. B) When the decay is instigated by a collision with a proton. C) As a beta particle is released, a neutron transforms into a proton. D) It is not possible. Radioactive decay always results in an isotope with the same or lower atomic number.
c
27) What is the name for the following polyatomic ion? CH3CO2- A) acidic B) acetic C) acetate D) monocarboxylate E) carboxylic
c
28) Many of the macroscopic properties of a compound depend on ________. A) the number of nucleons present in the sample B) how the atoms absorb light and the shape of the orbitals C) how the atoms of the molecules are held together D) the mass of the constituent atoms E) the size of the sample
c
29) Which of the following is not a property of metal? A) is strong, but can be bent B) conducts electricity C) does not conduct heat well D) is shiny E) All of the above are properties of metals.
c
4) If a nucleus of 232^ 90 Th absorbs a neutron and the resulting nucleus undergoes two successive beta decays (emitting electrons), what nucleus results? A) Plutonium-232 B) Americium-232 C) Uranium-233 D) Thorium-233
c
4) Why does an atom with many valence electrons tend to gain electrons rather than lose any? A) The old adage that ʺhe who has, getsʺ is also true in atomic structure. Atoms with many valence electrons can essentially overpower atoms with few valence electrons and attract additional electrons. B) There is stability in numbers. Atoms with many valence electrons are always attracting new electrons. C) Atoms with many valence electrons tend to have relatively strong forces of attraction between the valence electrons and the nucleus. This makes it easy for them to gain additional electrons. D) Atoms with many valence electrons tend to have relatively weak forces of attraction between the valence electrons and the nucleus. Therefore, the outer electrons are free to attract other electrons.
c
40) Which of the following would be an ion with a double positive charge? A) an Mg atom that loses one electron B) an Mg atom that gains two electrons C) an Mg atom that loses two electrons D) an Mg atom that gains one electron E) none of the above
c
44) Which are older, the atoms in the body of an elderly person or those in the body of a baby? A) a baby because this is surely a trick question B) an elderly person because they have been around much longer C) They are of the same age, which is appreciably older than the solar system. D) It depends upon their diet.
c
48) Carbon-14 dating is fairly reliable for dating once-living materials that died up to ________. A) 250.000 years ago B) 2.5 million years ago C) 50,00 years ago D) 5000 years ago
c
6) A neutron makes a better nuclear bullet than a proton or an electron because it ________. A) has the greatest mass B) can be accelerated by electromagnetic fields C) carries no electrical charge D) all of the above
c
7) Is it at all possible for a hydrogen nucleus to emit an alpha particle? A) yes, but it does not occur very frequently B) no, because it would require the nuclear fission of hydrogen, which is impossible C) no, because it does not contain enough nucleons D) yes, because alpha particles are the simplest form of radiation
c
8) Which of the following molecules should have the same molecular shape and approximate bond angles as ammonia, NH3? A) NO2 B) BH3 C) PH3 D) CH4 E) SO3
c
9) Which of the following sources of radiation provides most of our yearly exposure? A) televisions (cathode ray tubes) B) dental and medical X-rays C) background radiation D) smoke detectors E) living near nuclear power plants
c
28) Why does plutonium not occur in appreciable amounts in natural ore deposits? A) Most naturally occurring plutonium deposits have already been depleted in the creation of nuclear weapons. B) Plutonium loses electrons to form positively charged particles that have long since washed into the oceans. C) Any plutonium initially in the earthʹs crust has long since decayed. D) Plutonium is strictly a human-made element.
cd
1) Some people fear drinking distilled water because they have heard it leaches minerals from the body. What scientifically sound information might be offered to such a person? A) chill the distilled water to decrease its leaching potential B) add small amounts of salt to the distilled water before drinking it C) buy distilled water that has also undergone reverse osmosis D) Distilled water is relatively pure water, which loses its purity once it mixes with everything else in your stomach.
d
11) Which of the following statements best describes a relatively polar covalent bond? A) two very electronegative atoms undergo ionic bonding B) two very electronegative atoms are covalently bound C) two weakly electronegative atoms undergo ionic bonding D) a very electronegative atom and a weakly electronegative atom are covalently bound E) none of the above
d
12) Why will nuclear fission probably not be used directly for powering automobiles? A) Itʹs more practical for cars to use the electricity generated by nuclear fission power plants. B) Massive shielding would be required to protect against radioactivity exposure. C) Radioactive wastes could not be adequately controlled. D) All of the above are true.
d
13) Where did the atoms that make up a newborn baby originate? A) in the earth through geological processes B) in the digestion of the food that the mother ate C) in the womb of the babyʹs mother D) in the explosions of ancient stars
d
14) The strong nuclear force is very sensitive to ________. A) mass B) electromagnetism C) the weak nuclear force D) distance
d
15) What is the valence shell? A) It is the shell of electrons in element V (atomic no. = 23) B) It is the same as the orbital configuration. C) It is the last partially filled orbital in an atom. D) It is the outermost shell of electrons in an atom. E) It is the shell of electrons in an atom that is the least reactive.
d
17) Germanium chloride, GeCl2, has only two atoms surrounding the central germanium atom. Why then is the germanium chloride molecule bent? A) It is bent only periodically as it swings between both bent and linear shapes. B) Lone pairs of electrons on the chlorine atoms push it to this orientation. C) There is a covalent bond between the two chlorine atoms. D) A lone pair of electrons on germanium pushes it to this orientation.
d
19) If a nucleus of 232^ 90 Th absorbs a neutron and the resulting nucleus undergoes two successive beta decays (emitting electrons), what nucleus results? A) thorium-233 B) americium-232 C) plutonium-232 D) uranium-233
d
23) Which of the following provides the minimum amount of protection you need to block the following form of radiation? gamma A) thick leather B) suntan lotion C) T-shirt D) lead suit E) none of the above
d
3) There is more gold in 1 km3 of the ocean than the amount of gold mined in all of recorded history. How come we do not mine the oceans? A) It would cost too much. B) It would take too much energy. C) It is too dilute to separate. D) all of the above E) none of the above
d
30) What are some of the optimistic worldwide changes that may follow the advent of successful fusion reactors? A) There will be fewer hostilities between nations. B) Economies will be geared to relative abundance rather than scarcity. C) Humans will have more opportunities to focus on social issues, such as world hunger. D) all of the above
d
31) Why is the carbon-14 dating not accurate for estimating the age of materials more than 50,000 years old? A) Actually, carbon-14 dating is accurate back to around 5 million years ago. B) Living organisms are too decomposed after 50,000 years. C) This form of radioactive dating is only accurate back 1,400 years. D) The concentration of carbon-14 in a body after 50,000 years is too low.
d
33) Water, H2O, and methane, CH4, have about the same mass and differ by only one type of atom. Why is the boiling point of water so much higher than that of methane? A) The water molecule is less symmetrical than is the methane molecule. B) The electronegativity difference between oxygen and hydrogen is greater than the electronegativity difference between carbon and hydrogen. C) The oxygen of a water molecule has two lone pairs of electrons. D) all of the above
d
36) Radioactivity is a tendency for an element or a material to ________. A) emit light B) radiate heat C) emit electrons D) emit radiation E) glow in the dark
d
37) When food is irradiated with gamma rays from a cobalt-60 source, does the food become radioactive? Why? A) Yes. This is why irradiation with cobalt-60 is no longer approved by the FDA. B) Yes. However, the radioactivity resulting is well below the danger level established by the FDA. C) Yes and No. Although the gamma rays initiate the nuclear reaction the radioactivity does not show up until the food is ingested. D) No. The gamma rays do not have sufficient energy to initiate the nuclear reaction in the atoms of the food.
d
38) Which of the following bonds would be the most polar? A) C-Cl B) C-I C) C-Br D) C-F E) All are equally polar.
d
39) The half-life of carbon-14 is 5,730 years. A sample is found to have one -eighth the original amount of carbon-14 in it. How old is the sample? A) 4,5800 years B) 5,730 years C) 716 years D) 17,200 years E) none of the above
d
4) Which of the following material phases cannot form a solution? A) liquids B) gases C) solids D) All of the above can form solutions. E) None of the above can form solutions.
d
43) The valence electron of a sodium atom does not sense the full +11 of the sodium nucleus. Why not? A) There are two ʺnon-valence shellʺ electrons shielding the sodium nucleus from sensing it. B) Since the +11 charge is spread evenly around the entire spherical surface of the nucleus, the actual force of the charge in any given direction is greatly diminished. C) The distance from the nucleus to the loosely held lone valence electron varies greatly over time. So, the average sense of charge from the nucleus is considerably less than +11. D) There are two inner shells of electrons containing ten electrons shielding the sodium nucleus from sensing it.
d
44) Why is metal shiny? A) The electrons absorb each light wave. B) The electrons transmit most wavelengths of light. C) The electrons emit light due to electronic excitation. D) The loose electrons reflect most wavelengths of light. E) all of the above
d
8) Which of the following best describes a two-molar sucrose solution? A) two liters of solution that contains 1 mole of sucrose B) one liter of solution that contains 6.02 × 1023 molecules of sucrose C) one mole of sucrose dissolved in 2 liters of solution D) one liter of solution that contains 2 moles of water E) one liter of solution that contains 2 moles of sucrose
d
9) Ammonia, NH3, is more polar than is borane, BH3 because it ________. A) is less symmetrical than borane B) its hydrogens are not exactly opposite one another C) has a lone pair of electrons D) all of the above
d
12) Which of the following molecules has two pairs of nonbonding electrons on the central atom? A) BH3 B) CO2 C) H2O D) H2S E) C and D
e
2) Hard water contains excessive amounts of ________. A) fluoride ions B) water ions C) magnesium ions D) calcium ions E) Two of the above are the most appropriate answers.
e
3) Which of the following is the weakest form of interatomic attraction? A) a chemical bond B) a dipole-dipole interaction C) a dipole-induced dipole interaction D) an ion-dipole interaction E) an induced dipole-induced dipole interaction
e
41) Which of the following statements regarding a nucleon is true? A) The mass of a nucleon depends on which nucleus it is in. B) Attraction between nucleons changes their mass. C) Some of the mass of a nucleon can be converted into energy by splitting certain nuclei. D) both A and C E) all of the above
e
49) Which of the following is a positive ion? A) Ca2+ B) Al3+ C) Mg2+ D) Na+ E) all of the above
e
9) Why is it important to conserve fresh water? A) As the human population grows, so does our need for fresh water. B) There is little fresh water available to us on our planet. C) It is expensive to purify nonpotable water. D) all of the above
e
