If i= angle of incidence and r = angle of refraction, then the `ratio sini/sinr is`
I. A constant for a pair of medium.
II. Is called refraction index of medium 2 with respect to medium 1.
III. Is called absolute refractive index of medium 2.
IV. Varies with tempearture.

Options

A. I, II and III
B. II, III and IV
C. I,II and IV
D. I, III and IV

Answer

To solve the problem, we need to analyze the given statements about the ratio of the sine of the angle of incidence (i) to the sine of the angle of refraction (r), which is represented as \( \frac{\sin i}{\sin r} \).

### Step-by-Step Solution:

1. **Understanding Snell's Law**:
According to Snell's Law, the relationship between the angle of incidence and the angle of refraction is given by:
\[ n = \frac{\sin i}{\sin r} \]
where \( n \) is the refractive index of the second medium with respect to the first medium.

2. **Analyzing the Statements**:
- **Statement I**: "A constant for a pair of medium."
- This statement is true. The ratio \( \frac{\sin i}{\sin r} \) is constant for a given pair of media, meaning it does not change as long as the media remain the same.

- **Statement II**: "Is called refractive index of medium 2 with respect to medium 1."
- This statement is also true. The ratio \( \frac{\sin i}{\sin r} \) indeed represents the refractive index of medium 2 with respect to medium 1.

- **Statement III**: "Is called absolute refractive index of medium 2."
- This statement is false. The absolute refractive index of a medium is defined with respect to a vacuum, not another medium. Therefore, this statement is incorrect.

- **Statement IV**: "Varies with temperature."
- This statement is true. The refractive index can vary with temperature as the properties of the medium change with temperature.

3. **Conclusion**:
Based on the analysis:
- Statements I, II, and IV are correct.
- Statement III is incorrect.

### Final Answer:
The correct options are I, II, and IV.