Why radioactivity process is random?

When considering gravity acceleration and the force of acceleration, what must be true? a. the direction of acceleration must be perpendicular to the direction of the force. b. the direction of the force and the direction of acceleration must be the same as each other. c. the direction of the force and the direction of acceleration must be opposite of each other. d. the mass of the body must be the same as the acceleration of the body.

If two parallel light rays hit a mirror, they will not be parallel to each other after they reflect.

What are known as the properties of substances that describe a substance et does not change that substances?