Chemistry Q136 – AP-EAMCET 2026

Which oxide of nitrogen can damage the leaves of plants and retard the rate of photosynthesis, when it is present in higher concentration in air?

Clue 1 of 3: Plant Health and Air Pollution

Certain atmospheric pollutants, especially oxides of nitrogen, can have detrimental effects on plant physiology, including visible damage to leaves and impaired metabolic processes like photosynthesis.

🧠 Full Solution Path

Step 1: Analyze the Question✦ Active

The question asks to identify which oxide of nitrogen causes damage to plant leaves and retards photosynthesis when present in high concentrations in the air. This points to a common air pollutant known for its phytotoxic effects.

Step 2: Identify Common Nitrogen Oxide Pollutants○ Expand

The major oxides of nitrogen that contribute to air pollution are nitric oxide ( $N O$ ) and nitrogen dioxide ( $N O_{2}$ ). Nitrous oxide ( $N_{2} O$ ) is a potent greenhouse gas but is generally not considered a direct phytotoxicant in the same way $N O_{2}$ is. Dinitrogen trioxide ( $N_{2} O_{3}$ ) is relatively unstable and not a significant atmospheric pollutant causing widespread plant damage.

💡 Teacher's Secret Hint

Remember that $N O$ is often oxidized to $N O_{2}$ in the atmosphere, making $N O_{2}$ the more prevalent damaging form.

Step 3: Evaluate the Effects of Nitrogen Oxides on Plants○ Expand

1. **Nitric Oxide ( $N O$ ):** While a pollutant, its direct impact on plants is less severe than $N O_{2}$ . It primarily affects human respiratory systems and contributes to ozone formation. Its toxicity to plants is often indirect, through its conversion to $N O_{2}$ . 2. **Nitrogen Dioxide ( $N O_{2}$ ):** This is a well-documented phytotoxic pollutant. High concentrations of $N O_{2}$ are known to cause visible injury to plant leaves, such as necrosis (dead spots), chlorosis (yellowing), and bronzing. It significantly interferes with the photosynthetic process by damaging chloroplasts, reducing chlorophyll content, and inhibiting enzyme activities vital for photosynthesis. This leads to reduced growth and yield. 3. **Nitrous Oxide ( $N_{2} O$ ):** Primarily known as a greenhouse gas and ozone-depleting substance. It is not typically associated with direct acute plant damage like leaf necrosis or photosynthetic retardation at ambient pollutant levels. 4. **Dinitrogen Trioxide ( $N_{2} O_{3}$ ):** This compound is not a major atmospheric pollutant responsible for widespread plant damage.

💡 Teacher's Secret Hint

Focus on the direct and well-established impacts of each pollutant on plant health, rather than indirect or minor effects.

Step 4: Conclusion○ Expand

Based on the established harmful effects of nitrogen oxides on plants, nitrogen dioxide ( $N O_{2}$ ) is the specific oxide that causes damage to plant leaves and retards the rate of photosynthesis when present in higher concentrations in the air.

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Chemistry Question 136 – AP-EAMCET 2026

Clue 1 of 3: Plant Health and Air Pollution

🧠 Full Solution Path