In basic environmental science, which common greenhouse gas is made up only of hydrogen and oxygen atoms?

Introduction / Context:
Greenhouse gases are substances in the atmosphere that trap heat and keep the planet warm enough to support life. Common examples include carbon dioxide, water vapour, methane and ozone. Many school level questions test whether candidates can identify the chemical composition of these gases and distinguish between them based on their constituent elements. Here the focus is on recognising which greenhouse gas is composed solely of hydrogen and oxygen atoms.

Given Data / Assumptions:

The question asks specifically about a greenhouse gas that contains only hydrogen and oxygen.
The options given are methane (CH4), ozone (O3), water vapour (H2O) and nitric oxide (NO).
We assume standard chemical formulae where C stands for carbon, H for hydrogen, O for oxygen and N for nitrogen.
We also assume that the student is aware that water vapour is an important greenhouse gas in Earth's atmosphere.

Concept / Approach:
The approach is to examine the chemical formula of each option and check which one has only hydrogen and oxygen as elements. Methane contains carbon and hydrogen, ozone consists only of oxygen, and nitric oxide contains nitrogen and oxygen. Water, represented by H2O in its vapour form in the atmosphere, is the only gas among the options where the formula includes hydrogen and oxygen but no other element. Since water vapour is also a well known greenhouse gas, this double check confirms the choice.

Step-by-Step Solution:
Step 1: Write down the chemical formula for each option: CH4 for methane, O3 for ozone, H2O for water, and NO for nitric oxide. Step 2: Identify the elements in methane, which are carbon (C) and hydrogen (H). This includes carbon, so it does not meet the condition of only hydrogen and oxygen. Step 3: Look at ozone, O3, which contains only oxygen atoms and no hydrogen. This fails the condition of containing hydrogen. Step 4: Examine nitric oxide, NO, which is made of nitrogen (N) and oxygen (O), with no hydrogen present. Step 5: Check water vapour, H2O, which clearly contains hydrogen (H) and oxygen (O) only, fully satisfying the requirement of the question. Therefore, water vapour is the correct answer.

Verification / Alternative check:
From environmental science, we know that water vapour is actually the most abundant greenhouse gas in the atmosphere, even though carbon dioxide receives more attention in policy discussions. Its formula H2O is universally taught in chemistry and is easy to recognise. Cross referencing with basic chemistry confirms that none of the other listed gases meet the condition of containing only hydrogen and oxygen. This consistency in both chemistry and climate science notes verifies that water vapour is the intended answer.

Why Other Options Are Wrong:
Methane (CH4) contains carbon in addition to hydrogen, so it fails the only hydrogen and oxygen requirement. Ozone (O3) consists solely of oxygen and does not contain hydrogen at all. Nitric oxide (NO) is made up of nitrogen and oxygen, again violating the condition because it includes nitrogen rather than hydrogen. Although all of these gases can play roles in atmospheric chemistry, they do not match the specific elemental condition stated in the question.

Common Pitfalls:
A frequent mistake is to see the word greenhouse gas and immediately think of carbon dioxide or methane without reading the condition about chemical composition carefully. Another pitfall is to overlook water vapour as a greenhouse gas because it is often associated with the water cycle rather than greenhouse effect in everyday discussion. Students should remember that water vapour is a powerful greenhouse gas and that its simple formula helps identify it quickly in such questions.

Final Answer:
The common greenhouse gas that contains only hydrogen and oxygen atoms is water vapour (H2O).