Question

it is not necessary that all oxidising agents should contain oxygen justify the statement

Answer 1

No. Take the reaction:

2HCl + 2Na → 2NaCl + H₂

In this, the hydrochloric acid was the oxidising agent. The sodium atoms donated an electron to the hydrogen ions to make them hydrogen atoms, making HCl the oxidising agent.

The confusion likely stems from different definitions of oxidation. In this context, oxidation means the loss of electrons, and oxygen, despite the name, has nothing to do with it.