Explain the following: Concentrated nitric acid appears ______when it is left standing in a glass bottle.

Explanation

**Step-by-Step Solution:**

1. **Understanding Concentrated Nitric Acid**: Concentrated nitric acid (HNO₃) is a strong acid that is known for its oxidizing properties. It is typically colorless when fresh.

2. **Decomposition of Nitric Acid**: When concentrated nitric acid is left standing in a glass bottle, it can undergo thermal decomposition. This means that the acid breaks down into other substances over time.

3. **Chemical Reaction**: The decomposition reaction can be represented as follows:
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