Which statement about gases is true

This question is incomplete. The completed question is below

Which statement about gases is true? A. They are made up of particles that always move very slowly. B. They are made up of particles that travel in a curved path when in motion. C. They are made up of hard spheres that vibrate quickly in stationary positions. D. They are made up of hard spheres that are in random motion.

The correct option is D

Explanation:

There are three states of matter; solid, liquid and gas. Matter in gaseous state have particles that are not tightly packed and hence move freely. They have no definite shape but assume the shape of the container they are stored. These particles move randomly colliding against one another and the wall of the container they are stored. There collision with one another does not mean they will react with one another - this is because of there hard spherical structure.

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.