Which sample of matter is a mixture? air, water, ammonia

Which sentence about particles in matter is true? a. atoms are present in solids and liquids but not in gases. b. the particles of matter are in constant motion. c. the same kinds of atoms are found in different elements. d. when a solid changes to a liquid, the sizes of the particles change.

What must occur for air masses to form fronts

Will mark brainliest how many electrons can be held in the energy level n = 4?