Basically when frozen water/ice crystals high in the atmosphere collect water vapor molecules they grow. They are sometimes supplied by microscopic cloud droplets.
C
Why? As you increased energy levels the distance between two energy levels gets larger. This is often due to shielding
Answer:
Oxygen = 15.999 g/mol
Iron = 3 × 55.845 = 167.535 g/mol
CaCO3 = 20 × 100.0869 = 2001.738 g/mol