Question

Observe the following statements
Statement-I: The carbon containing components of photochemical smog are acrolein, methanal and PAN
Statement-II: The number of greenhouse gases in the list given below is 5
$\text{CH}_4, \text{CO}_2, \text{NO}, \text{H}_2\text{O}(\text{l}), \text{H}_2\text{O}(\text{g}), \text{O}_2, \text{O}_3$
The correct answer is

• A. Both statements I and II are correct
• B. Both statements I and II are not correct
• C. Statement I is correct, but statement II is not correct
• D. Statement I is not correct, but statement II is correct

Hint:

Photochemical smog involves a mix of primary and secondary pollutants. The major GHGs are water vapor ($\text{H}_2\text{O}$), carbon dioxide ($\text{CO}_2$), methane ($\text{CH}_4$), nitrous oxide ($\text{N}_2\text{O}$), and ozone ($\text{O}_3$). Diatomic gases of the same element, like $\text{O}_2$ and $\text{N}_2$, are not greenhouse gases.

Answer 1

The Correct Option is C

Step 1: Analyze Statement-I (Components of Photochemical Smog).
Photochemical smog is formed from the reaction of sunlight with nitrogen oxides and volatile organic compounds (VOCs) in the atmosphere.
The carbon-containing components that are products of this process include:
- Acrolein ($\text{CH}_2=\text{CHCHO}$).
- Methanal (Formaldehyde, $\text{HCHO}$).
- PAN (Peroxyacyl nitrates, e.g., $\text{CH}_3\text{COOONO}_2$).
The statement listing acrolein, methanal, and PAN as carbon-containing components of photochemical smog is correct.

Step 2: Analyze Statement-II (Number of Greenhouse Gases).
Greenhouse gases (GHGs) are those gases in the Earth's atmosphere that absorb and emit radiation within the thermal infrared range, causing the greenhouse effect. They include compounds that contain at least two different atoms (diatomic molecules like $\text{O}_2, \text{N}_2$ are generally not GHGs).
The list is: $\text{CH}_4, \text{CO}_2, \text{NO}, \text{H}_2\text{O}(\text{l}), \text{H}_2\text{O}(\text{g}), \text{O}_2, \text{O}_3$.
- $\text{CH}_4$ (Methane): A potent GHG. ($\checkmark$)
- $\text{CO}_2$ (Carbon Dioxide): The most significant human-caused GHG. ($\checkmark$)
- $\text{NO}$ (Nitric Oxide): Not a primary GHG in the context of global warming (its dimer $\text{N}_2\text{O}_4$ and $\text{N}_2\text{O}$ are, but $\text{NO}$ is mostly involved in photochemical reactions). However, in many lists, $\text{NO}$ is often considered a short-lived radiative-forcing agent. $\text{N}_2\text{O}$ (Nitrous Oxide) is a major GHG. Assuming the question intended the major GHGs: $\text{NO}$ is not typically counted as a major GHG. Let's assume it's not a GHG.
- $\text{H}_2\text{O}(\text{l})$ (Liquid Water): Water vapor is a GHG, but liquid water is not a gas. ($\times$)
- $\text{H}_2\text{O}(\text{g})$ (Water Vapor): A major natural GHG. ($\checkmark$)
- $\text{O}_2$ (Oxygen): Not a GHG. ($\times$)
- $\text{O}_3$ (Ozone): A GHG (both tropospheric and stratospheric). ($\checkmark$)
The greenhouse gases in the list are $\text{CH}_4, \text{CO}_2, \text{H}_2\text{O}(\text{g}), \text{O}_3$. This is a count of 4.
The statement claims the number is 5. Therefore, Statement-II is not correct.

Step 3: Conclude the final answer.
Statement I is correct, but Statement II is not correct.