Which of the following nations has the maximum per capita emissions of carbon…

Concept — what "per capita" means. Per capita CO2 emission = a country’s total annual CO2 emission ÷ its population. It is an average taken over every resident, so it measures how carbon-intensive one person’s energy use is — not how large the country’s overall output is. Two consequences follow directly from that division: a very populous country can lead the total-emission table and still sit low on the per capita table, because the same volume is shared by far more people; and a less populous country whose residents each consume a lot of fossil fuel can lead the per capita table without leading the total.

Application. Dividing each nation’s annual CO2 output by its population gives the following averages (World Bank / IEA data):

Cross-check — total versus per capita. China releases the largest total volume of CO2 of any country, but that volume is divided among roughly 1.4 billion people, which pulls its per-person figure below the American one. India has a comparable population with far lower per-person energy use, so it sits lowest of the four. The two rankings therefore disagree, and that disagreement is exactly what this question tests. The ordering is not a recent accident: when this paper was set in 2013 the per-person figures were USA ≈ 16.2 t, Japan ≈ 9.7 t, China ≈ 6.7 t and India ≈ 1.5 t, giving the same leader.

Result. Among the four nations listed, the USA has the maximum per capita carbon dioxide emissions.