What makes alkali metal halides sometimes coloured which are othersise colourless ?

Explanation

To understand why some alkali metal halides are colored while others are colorless, we can break down the explanation into several steps:

### Step-by-Step Solution:

1. **Identify Alkali Metal Halides**:
- Alkali metal halides include compounds like NaCl (sodium chloride), KCl (potassium chloride), and LiCl (lithium chloride). Typically, these compounds are colorless.

2. **Understand the Concept of Color**:
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