According to the law of reflection:

Options

A. `i//r=` constant
B. `sin I // sin r=` constant
C. `i+r=` constant
D. `i=r`

Answer

### Step-by-Step Solution:

1. **Understanding the Law of Reflection**: The law of reflection states that when light reflects off a surface, the angle of incidence (the angle at which the incoming light ray strikes the surface) is equal to the angle of reflection (the angle at which the light ray reflects off the surface).

2. **Identifying the Statements**: The question presents four statements regarding the law of reflection:
- (A) I by R equal to constant
- (B) sin I by sin R equal to constant
- (C) I + R equal to constant
- (D) I equal to R

3. **Analyzing Each Statement**:
- **Statement A**: I/R = constant. This is incorrect because the law of reflection does not state that the ratio of the angles is constant.
- **Statement B**: sin I/sin R = constant. This is also incorrect; the law of reflection does not involve sine functions in this context.
- **Statement C**: I + R = constant. This is incorrect as well; the law does not state that the sum of the angles is constant.
- **Statement D**: I = R. This is correct as per the second law of reflection, which states that the angle of incidence is equal to the angle of reflection.

4. **Conclusion**: The correct answer is **Statement D (I = R)**, as it directly reflects the second law of reflection.