What is the angle of repose?
a. the angle of bedding on hills where layers dip parallel to the slope
b. the angle of fractures on hills where fractures dip parallel to the slope
c. the angle at which rainfall strikes an unstable slope
d. the steepest angle at which loose material remains stable

option (d)

Explanation:

The minimum angle of inclination of the inclined plane from the horizontal such that the object placed on the inclined plane is just start sliding down.

The value of angle of repose is given by the

tan θ = μ

Where, θ be the angle between the horizontal plane and the inclined plane and μ be the coefficient of friction.

It is also called as the angle of sliding.

a skateboard rolling across the street - apex