Thunderstorm can be beneficial to plants because it

Step 1: Analyze the question We need the benefit of a thunderstorm to plants. This links to the nitrogen cycle.

Step 2: The concept Air is about 78% nitrogen gas (N₂), which plants cannot use directly. During a thunderstorm, lightning supplies enough energy to make nitrogen and oxygen in the air combine:

• N₂ + O₂ → 2NO (nitric oxide), under the high temperature of lightning
• 2NO + O₂ → 2NO₂ (nitrogen dioxide)
• 4NO₂ + 2H₂O + O₂ → 4HNO₃ (nitric acid), which dissolves in rainwater

The nitric acid falls with the rain and reacts with minerals in the soil to form nitrates. Plants absorb nitrates through their roots and use them to make proteins. This process is called atmospheric nitrogen fixation.

Step 3: Check the options

• A. Adds lime to the soil: Wrong. Lightning does not add calcium compounds. (Lime is used to reduce soil acidity.)
• B. Kills pests: Wrong. This is not a reliable or direct effect.
• C. Destroys some major crops: This is harmful, not beneficial.
• D. Adds nitrate to the soil: Correct. It matches the nitrogen-fixation process above.

Answer: D, adds nitrate to the soil.

Exam tip: Remember "Lightning = Nitrogen fixing". Whenever you see thunderstorm or lightning in a Biology or Agric question about plants, think nitrates. The three ways nitrogen is fixed are: lightning, nitrogen-fixing bacteria (e.g. Rhizobium in legume root nodules), and industrial fertilizer production (Haber process).