Which of the following countries was the largest emitter of CO2 in 2015?

The correct answer is A, China. In 2015, China was the world's largest annual emitter of carbon dioxide from fossil fuels, releasing roughly 9 billion tonnes, which was nearly double the figure for the United States. China has held this top spot in annual emissions since the mid-2000s, and the gap has remained large.

• U.S.A (B): The US was the second-largest annual emitter in 2015, at about 5 billion tonnes. It remains the largest historical (cumulative) emitter since industrialisation, which is why aspirants sometimes mix up the two measures.
• India (C): India was the third-largest emitter that year, at about 2 billion tonnes. Its per-capita emissions are far below those of the US or China.
• France (D): France emitted only a few hundred million tonnes, thanks to its large nuclear share in electricity generation.

The core concept here is the distinction between annual, cumulative and per-capita emissions, as tracked by bodies like the Global Carbon Project. For Mains GS-III (Environment), this links to the Paris Agreement and the principle of common but differentiated responsibilities and respective capabilities (CBDR-RC), which frames the debate on climate finance and equity.

Trap: Aspirants often pick the US because it is the biggest historical emitter. Read whether the question asks about a single year, a cumulative total, or per capita.