Assertion : All halogens are coloured.
Reason : The halogens absorb visible light .

Options

A. If both the assertion and reason are true and reason is correct explanation of the assertion .
B. If both the assertion and reason are true but reason is not a correct explanation of the assertion .
C. If the assertion is true but the reason is false.
D. If both assertion and reason are false.

Explanation

To solve the question, we need to analyze the assertion and the reason provided:

**Assertion**: All halogens are coloured.
**Reason**: The halogens absorb visible light.

### Step-by-Step Solution:

1. **Identify the Halogens**: The halogens are a group of elements found in Group 17 of the periodic table. They include fluorine (F), chlorine (Cl), bromine (Br), and iodine (I).

2. **Color of Halogens**:
- **Fluorine (F2)**: Pale yellow
- **Chlorine (Cl2)**: Yellowish-green
- **Bromine (Br2)**: Reddish-brown
- **Iodine (I2)**: Deep violet

From this, we can see that all halogens exhibit some form of color, confirming that the assertion is true.

3. **Understanding the Reason**: The reason states that halogens absorb visible light. This is indeed correct because the colors we observe in these halogens are due to their ability to absorb certain wavelengths of visible light. When they absorb light, electrons in the halogen molecules get excited from a lower energy level (HOMO - Highest Occupied Molecular Orbital) to a higher energy level (LUMO - Lowest Unoccupied Molecular Orbital).

4. **Conclusion**: Since both the assertion and the reason are true, and the reason correctly explains why the assertion is true, we conclude that the correct answer is:

**Option A**: Both the assertion and reason are true, and the reason is the correct explanation of the assertion.