B. explain why it is more difficult to move an object at rest, than to keep an object moving
with uniform motion.

because the static friction is higher than the kinetic friction

Explanation:

Inertia is resistance to motion. Object resist changing its current motion or the rest position. This is the Newton's first law of motion

apart from this as the graph shows , the force needed to move when object at rest is higher than the force to change the motion of a moving body . this is because

static friction > kinetic friction

d) physical means can be used to separate the components of air.

the order for strong to weak forces such as

strong nuclear force → electromegnetic force → weak nuclear force → gravitational force

the fundamental forces are those forces that act between to objects or element to make interactions. there are four types of fundamental forces such as strong and weak nuclear forces (due to protons and electrons), electromagnetic force (due to the motion of electrons) and gravitational force (due to orbital movement of the planet). if these forces are arranged on the basis of their maximum strength then the order is

strong nuclear force → electromegnetic force → weak nuclear force → gravitational force