Why can we see the entire side of the moon during a full moon?

Its because instead of the sun being behind the earth therefor causing a shadow on the moon, it is away from the earth or behind the moon causing an eclipse.

Explanation: When the shadow of the earth is on the moon, it causes a shadow on the moon because the earth is a sphere. When the sun rotates away from the moon it prevents a shadow on the moon. Therefore causing a full moon and letting us see the entire side of the moon.

c. magnitude and direction

electric field is a function of 1/r^2

yes, the force per unit charge for a point charge is inverse square law.