If 135 grams of MgCl2 are dissolved in a 1.0 L solutions, what is the molarity of the solution?

In a sample of oxygen gas at room temperature, the average kinetic energy of all the balls stays constant. which postulate of kinetic molecular theory best explains how this is possible? a. attractive forces between gas particles are negligible because the particles of an ideal gas are moving so quickly. b. collisions between gas particles are elastic; there is no net gain or loss of kinetic energy. c. gases consist of a large number of small particles, with a lot of space between the particles. d. gas particles are in constant, random motion, and higher kinetic energy means faster movement.

Iknow the answer is a but i don't know why

Summarize possible ways in which phases of matter could combine to form a solution.