A substance has critical angle of `45^(@)` for yellow light. What is its refractive index ?

Explanation

To find the refractive index of a substance given its critical angle, we can use Snell's law and the definition of the critical angle.

### Step-by-Step Solution:

1. **Understand the Concept of Critical Angle**:
The critical angle (θc) is the angle of incidence in the denser medium (substance) at which the angle of refraction in the less dense medium (air) is 90 degrees.

2. **Use the Formula for Critical Angle**:
...