Correct Option (D)
Statement 1 asserts, "None but the rich can afford air-travel." This logically implies that the ability to travel by air is exclusively possessed by the rich. Consequently, if an individual is observed traveling by air, it must be concluded that they are rich. Therefore, all individuals who undertake air travel are, by definition of the statement, rich.
Incorrect Options:
Option (A) All the rich persons travel by air: This conclusion cannot be drawn. Statement 1 indicates that only the rich can afford air travel, but it does not state that all rich individuals actually choose to travel by air. A rich person may opt for other modes of transport or not travel at all.
Option (B) Those who travel by air become sick: This conclusion is not supported. Statement 2 explicitly states, "Some of those who travel by air become sick." The term "some" indicates a subset, not the entirety, of air travelers. Therefore, it cannot be inferred that all who travel by air become sick.
Option (C) All the rich persons become sick: This conclusion is unfounded. While Statement 1 links air travel to richness and Statement 2 links some air travelers to sickness, there is no premise that connects all rich persons directly to becoming sick. The chain of inference does not extend to encompass all rich individuals.