The correct answer is option 3, which states that both statements I and II are correct.

Statement I is true, as nuclear winter is indeed a term used to describe the predicted climatic effects of nuclear war. It is based on the hypothesis that the massive amounts of smoke, dust, and soot generated by a nuclear exchange would block sunlight, leading to a significant drop in temperatures and severe disruptions in climate patterns.

Statement II is also true, as mentioned in a 2008 study published in the proceedings of the National Academy of Science, USA. The study found that a nuclear exchange between Pakistan and India using their current arsenals could lead to the creation of a near-global ozone hole, which could cause human health problems and have severe environmental consequences for at least a decade.

Therefore, both statements correctly describe the potential consequences of a nuclear weapons exchange, making option 3 the correct answer.