Which of the following is used in rocket propellants?

Correct answer: (d) All of the above

Explanation

A rocket propellant has a fuel and an oxidiser. All three are used:

• hydrazine (N₂H₄): a liquid fuel, also used alone in small thrusters on satellites;
• liquid oxygen (O₂): the most common oxidiser;
• liquid hydrogen (H₂): a high-energy cryogenic fuel. India's cryogenic engines burn liquid hydrogen with liquid oxygen.