The electric spark produced during lightening helps nitrogen to combine with oxygen to forn itric oxide.

Explanation

**Step-by-Step Text Solution:**

1. **Understanding the Reaction**: During a lightning strike, an electric spark generates a high temperature and pressure in the atmosphere. This environment is conducive for chemical reactions to occur.

2. **Nitrogen and Oxygen in the Atmosphere**: The atmosphere is primarily composed of nitrogen (about 78%) and oxygen (about 21%). Under normal conditions, these gases do not react with each other.

3. **Role of Lightning**: The electric spark from lightning provides the energy needed to break the strong bonds between nitrogen molecules (N₂) and oxygen molecules (O₂).

4. **Formation of Nitric Oxide**: When the nitrogen and oxygen molecules come into contact with the energy from the lightning, they can combine to form nitric oxide (NO). The chemical reaction can be represented as:
\[ N_2 + O_2 \xrightarrow{lightning} 2NO \]

5. **Importance of Nitric Oxide**: Nitric oxide is an important compound in the atmosphere. It can further react with oxygen to form nitrogen dioxide (NO₂), which can contribute to the formation of acid rain.

6. **Conclusion**: Thus, the electric spark from lightning plays a crucial role in the nitrogen-oxygen reaction, leading to the formation of nitric oxide, which has significant environmental implications.

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