Newton's first law of motion states that a body at rest will remain at rest, and a body in motion will continue in motion with the same speed and in the same direction unless acted upon by a net external force. Therefore, the statement "a body at rest will move if a force is applied to it" is true in the context of Newton's first law.
The other statements listed are inaccurate in relation to Newton's first law. Diffusion is a separate concept from Newton's laws of motion and involves the movement of molecules from an area of higher concentration to an area of lower concentration, but this is not related to Newton's first law.
So, the true statement in relation to Newton's first law is: "a body at rest will move if a force is applied to it."