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The most common metal in the Earth’s crust, aluminum (or aluminium) was not discovered until 1825 because its isolated state is so reactive that free nuggets or flakes of the metal are never found in nature; rather, the metal is typically found as part of an amalgam, most commonly bauxite ore. Moreover, elemental aluminum is extremely difficult—and expensive—to separate from its ores by traditional chemical means. Indeed, the extreme reactivity of aluminum helps protect its modern, ubiquitous manifestations, such as aluminum foil. The surface of pure aluminum instantly combines with atmospheric oxygen to form a thin but robust “passivization” seal of aluminum oxide that prevents further corrosion. Many other metals, such as iron, are less reactive than aluminum, but their superficial oxides do not form as swiftly, completely, or impermeably.
For several decades after its discovery, aluminum was considered a precious metal and was more costly than gold or platinum, not because of any fundamental scarcity, but because of its elevated cost of production. The price of aluminum suddenly plummeted in 1886, however, when two 23-year-old inventors independently developed an electrolytic process of separating pure aluminum from a bath of molten aluminum salts, primarily cryolite. Cryolite itself is rare enough that synthetic salts eventually replaced it as the solution medium.
1. What can be most logically inferred from the passage about iron?
(A) It corrodes more quickly than aluminum.
(B) Its oxides form more slowly and robustly than those of aluminum.
(C) It is cheaper to isolate from its ores by traditional chemical means than aluminum.
(D) It is more susceptible to passivization than is aluminum.
(E) It is more commonly found in its isolated, elemental state.
2. According to the passage, the natural passivization layer on the surface of aluminum metal
(A) causes atmospheric oxygen to react chemically with the metal
(B) is less impenetrable than typical iron oxide films formed on pure iron
(C) lowers the utility of aluminum in its uncontaminated state
(D) provides aluminum with a chemical advantage, relative to other metals (E) precludes the inexpensive purification of the metal by traditional chemical processes
3. In terms of economic impact, which of the following hypothetical situations would be most analogous to what the passage indicates happened in 1886?
(A) Fossil remains of a previously unknown dinosaur species are simultaneously discovered by two researchers working independently of one another.
(B) Lead-acid batteries are widely replaced in automobiles by batteries containing lithium, a much rarer metal than lead.
(C) Direct processing of light signals within fiber-optic devices supplants electronic signal processing performed by solid-state transistors.
(D) After supplies of a widely used commodity become unavailable, the price of the commodity surges.
(E) Low-cost artificial synthesis of diamonds, which are expensive to mine but composed of the common element carbon, is perfected.
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发表于 2021-4-14 15:54:46
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