Which of the following is a set of greenhouse gases?

First, recall the basic definition: a greenhouse gas is one that absorbs infrared radiation and contributes to the greenhouse effect, thereby warming the Earth’s atmosphere. Classic examples, stated in every standard textbook, are $$CO_2$$, $$CH_4$$, $$N_2O$$, $$O_3$$, water vapour, CFCs, and a few others. In contrast, gases like $$N_2$$ and $$O_2$$ make up most of the air but do not absorb infrared radiation appreciably, while gases such as $$SO_2$$ and $$Cl_2$$ may cause pollution or participate in other atmospheric chemistry without being major greenhouse contributors.

Now we examine each option one by one and test whether every gas listed truly belongs to the greenhouse category.

Option A presents $$O_3$$, $$NO_2$$, $$SO_2$$, $$Cl_2$$. We recognise $$O_3$$ as a greenhouse gas, but $$NO_2$$ is chiefly an air pollutant tied to photochemical smog, $$SO_2$$ leads to acid rain, and $$Cl_2$$ is not a greenhouse gas at all. Because three of the four gases fail the definition, the entire set is disqualified.

Option B gives $$CH_4$$, $$O_3$$, $$N_2$$, $$SO_2$$. Here $$CH_4$$ and $$O_3$$ do fit, yet $$N_2$$ is the principal inert component of air with negligible infrared absorption, and $$SO_2$$ again is mainly a pollutant. Since two entries are non-greenhouse, this set is also incorrect.

Option C lists $$CO_2$$, $$CH_4$$, $$N_2O$$, $$O_3$$. Each one of these gases is explicitly named in the Intergovernmental Panel on Climate Change (IPCC) reports as a greenhouse gas: $$CO_2$$ is the benchmark, $$CH_4$$ is the second-most discussed, $$N_2O$$ ranks third in potency, and $$O_3$$ acts both in the troposphere and stratosphere. Because every member of the set satisfies the required property, Option C stands correct.

Option D proposes $$O_3$$, $$N_2$$, $$CO_2$$, $$NO_2$$. While $$O_3$$ and $$CO_2$$ are acceptable, $$N_2$$ once again is not a greenhouse gas, and $$NO_2$$ plays only a marginal infrared role compared with its importance in smog chemistry. Therefore this set is also invalid.

Comparing all four possibilities, only Option C contains a collection where each gas is undeniably a greenhouse gas. Hence, the correct answer is Option 3.