When sodium or potassium is dropped in water, we can observe a golden yellow or a lilac coloured flame, respectively, whereas when calcium is dropped, no flame is observed. Why is there a difference in observation in the above two cases?

Explanation

### Step-by-Step Solution:

1. **Understanding the Elements**: Sodium (Na) and potassium (K) are alkali metals, while calcium (Ca) is an alkaline earth metal. Sodium has an atomic number of 11, potassium has an atomic number of 19, and calcium has an atomic number of 20.

2. **Electronic Configuration**:
- Sodium: 1s² 2s² 2p⁶ 3s¹ (1 valence electron)
- Potassium: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ (1 valence electron)
- Calcium: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 4s² (2 valence electrons)
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