Concentrated nitric acid renders aluminium passive. Give reasons.

Explanation

### Step-by-Step Solution:

1. **Understanding the Reaction**: When concentrated nitric acid (HNO3) is added to aluminum (Al), a chemical reaction occurs. This reaction is significant because it leads to the formation of a protective layer on the surface of aluminum.

2. **Formation of Alumina**: The concentrated nitric acid reacts with aluminum to form aluminum oxide (Al2O3), commonly known as alumina. The chemical equation for this reaction can be represented as:
\[ 4Al + 6HNO_3 \rightarrow 2Al_2O_3 + 6NO_2 + 3H_2O \]
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