Assertion (A): In a motion picture, usually 24 frames are projected every second over the whole length of the film. Reason (R): An image formed on the retina of eye persists for about 0.1 s after the removal of stimulus.

The correct option is A because both statements are true and the reason directly explains the assertion.

Assertion A is true because 24 frames per second is the standard frame rate used in motion pictures to create the illusion of smooth, continuous movement.

Reason R is true because of a phenomenon called persistence of vision. When an image is formed on the retina, it stays there for about 0.1 to 0.16 seconds even after the object is removed.

The reason explains the assertion because if frames are projected faster than the eye can clear the previous image which is 24 frames per second being much faster than the 0.1 second decay, the brain blends the individual still images together. This creates the perception of motion rather than a series of flickering photos.