Introduction:
When a ray of light is incident on a mirror, it gets reflected according to the laws of reflection. In this scenario, we have two mirrors, A and B, placed at right angles to each other. We need to calculate the angle of reflection for the ray that is reflected from mirror B after it has been incident on mirror A at an angle of 25 degrees.

Laws of Reflection:
Before we proceed with the calculation, let's understand the laws of reflection. When a ray of light strikes a smooth and polished surface, the following laws apply:
1. The incident ray, the reflected ray, and the normal (a line perpendicular to the surface at the point of incidence) all lie on the same plane.
2. The angle of incidence (θi) is equal to the angle of reflection (θr), measured between the incident ray and the normal.

Calculation:
1. Angle of Incidence on Mirror A: The ray of light is incident on mirror A at an angle of 25 degrees. This angle is measured between the incident ray and the normal to mirror A. Let's denote this angle as θiA.

2. Reflection from Mirror A: According to the laws of reflection, the angle of reflection from mirror A will be equal to the angle of incidence. Therefore, the angle of reflection from mirror A, denoted as θrA, will also be 25 degrees.

3. Angle between Mirror A and Mirror B: Since mirror A and mirror B are placed at right angles to each other, the angle between them is 90 degrees.

4. Angle of Incidence on Mirror B: After reflection from mirror A, the ray of light falls on mirror B. The angle of incidence on mirror B, denoted as θiB, will be equal to the angle between mirror A and mirror B subtracted from the angle of reflection from mirror A.
θiB = 90 degrees - θrA
θiB = 90 degrees - 25 degrees
θiB = 65 degrees

5. Angle of Reflection from Mirror B: According to the laws of reflection, the angle of reflection from mirror B will be equal to the angle of incidence on mirror B. Therefore, the angle of reflection from mirror B, denoted as θrB, will also be 65 degrees.

Conclusion:
The angle of reflection for the ray of light reflected from mirror B is 65 degrees.