Which of the angles shown in this picture is the angle of incidence? a b

The pictures are not attached, therefore, I cannot give a specific choice.
However, I will try to help you out.

The angle of incidence is defined as the angle formed between the ray of light and the normal to the surface that the ray is falling on.

The angle of incidence can be shown in the attached image.

Therefore, for your question, choose the image on which the above description applies.

Hope this helps :)

The third hammer 8 pounds