What is the oxidizing agent used in most rockets and missiles?

An oxidizing agent is needed for the combustion of the
fuel in a rocket. The combustion of the fuel generates a lot of energy which pushes out
the products of combustion with a very high momentum in the backward direction. An equal
reaction to this action pushes the rocket forward.

There
are many oxidizing agents that are used for rockets which differ based on the size of
the rocket, the type of fuel being used, where the rocket is going to be flying, how
fast it has to be made ready to fly, etc.

Usually the
oxidizing agent is oxygen or a compound that releases oxygen when it is heated or
undergoes another reaction prior to the oxidation of the fuel. Though there is oxygen
present in the air, rocket fuels require a lot of oxygen and have to burn at a very fast
rate. This makes it essential to keep the source of oxygen with the fuel. Oxygen based
oxidizing agents include liquid oxygen, hydrogen peroxide, nitric acid, potassium
nitrate, etc.

Other oxidizing agents are fluorine,
chlorine, sulfur and their compounds like bromine fluoride, carbon fluoride,
etc.