Condensation – the process of water vapor turning back into liquid water, with the best example being those big, fluffy clouds floating over your head.
Oxygen – a chemical element that constitutes 21 percent of the Earth’s atmosphere. It is capable of combining with all elements except some noble gases, is active in physiological processes of almost all known organisms, and is involved especially in combustion.
Hydrogen – a nonmetallic gaseous chemical element with atomic number 1 that is the simplest and lightest of the elements . It is used especially in the processing of fossil fuels and the synthesis of ammonia.
Sometimes there is rain without clouds, but this is generally because the wind is blowing the rain from a cloud that may not be visible where you are.