Which gas in the atmosphere is essential for respiration?

Explanation

**Step-by-Step Solution:**

1. **Understanding Respiration**: Respiration is a biological process through which living organisms produce energy by breaking down food. This process is crucial for survival.

2. **Cellular Respiration**: This is a specific type of respiration that occurs at the cellular level. During cellular respiration, glucose (C6H12O6) is broken down to release energy.

3. **Role of Oxygen**: For cellular respiration to occur, oxygen is required. Oxygen gas (O2) is essential as it helps in the breakdown of glucose into carbon dioxide (CO2), water (H2O), and adenosine triphosphate (ATP), which is the energy currency of cells.

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