B) Lead-acid batteries are widely replaced in automobiles by batteries containing lithium, a much rarer metal than lead.

We do not want another form or a better material to substitute or else

We want the SAME material that costs LESS and so is more convenient to produce

All the answer choices but E say to replace something. We do not have to replace the material. we want a scenario in which the SAME material is produced cost-effectively


I hope now is more clear. Read always careful.

Every word counts - count every word!

For Q1, WHY NOT OPTION C?

Question 1

A - The natural passivisation layer on the surface of aluminium metal, formed as a result of the surface of pure aluminium instantly combining with atmospheric oxygen, causes atmospheric oxygen to react chemically with the metal. Clearly incorrect, the passivisation layer forms as a result of the reaction, it does not cause the reaction.

B - The thin but robust natural passivisation layer on the surface of aluminium metal is less impenetrable (i.e. more penetrable) than typical oxide films, which do not form as swiftly, completely, or impermeably, formed on pure iron. Direct contradiction between the conclusion and the premise. How can the passivisation layer on aluminium be more robust, but also more penetrable, than that of iron.

C - The natural passivisation layer on the surface of aluminium metal, enabling aluminium's modern, ubiquitous manufestations, such as aluminium foil, lowers the utility of aluminium in its uncontaminated state. Firstly, the utility of aluminium in its uncontaminated state is not mentioned in the passage. Secondly, the layer increases the utility of aluminium. This answer choice couldn't be more wrong.

D - The thin but robust natural passivisation layer on the surface of aluminium metal, preventing further corrosion, provides a chemical advantage relative to other metals, whose superficial oxides do not form as swiftly, completely, or impermeably. This looks reasonable.

E - The natural passivisation layer on the surface of aluminium metal, formed as a result of the surface of pure aluminium instantly combining with atmospheric oxygen, precludes the inexpensive purification of the metal by the traditional chemical process. The passage does not contain any information that suggests that the passivisation layer is the reason for expensive purification by the traditional chemical process.

Answer is : D

Question 2


To draw an economic comparison or analogy between what happened in 1886 (according to the passage) and a hypothetical situation, we first need to understand the significance of the stated events in that year. The passage tells us that, in 1886, two inventors developed a new process to isolate aluminum, and that as a result the price plummeted. We might predict that we are looking for a situation in which a previously expensive product suddenly becomes cheaper because of a new technology or process.

(A) While this situation captures a couple of the features of the events of 1886 (two researchers working independently make a discovery at the same time), these features do not imply anything about the economic impact of that discovery.

(B) This situation is in some ways opposite to the events of 1886. In this choice, a product containing one material (lead) is replaced by a product containing a “much rarer” material (lithium); if anything, we would expect the price of the product to go up, not down.

(C) In this choice, nothing is indicated or implied about the economic impact of replacing an old process (electronic signal processing) with a new process (direct processing of light signals). We do not know whether the new process would be cheaper or more expensive.

(D) This situation is in some ways opposite to the events of 1886. Here, a commodity becomes scarce, and the price shoots up.

(E) CORRECT. Expensive diamonds become less expensive due to the perfection of a new technological process: “low-cost artificial synthesis.” This situation would be directly analogous, in terms of economic impact, to what happened with aluminum in 1886.

Answer: E

Question 3

The most common metal in the Earth’s crust, aluminum (or aluminum) 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. 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 impermeable.

For several decades after its discovery, aluminum was considered a precious metal, 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.

From the above highlighted portions clearly the answer is C