Final answer:
Arjun is not a missile in the Indian missile program; it is a main battle tank. The Agni, Trishul, and Prithvi are part of India's missile arsenal.
Step-by-step explanation:
The missile that is not a part of the Indian missile programme is the Arjun. The Agni, Trishul, and Prithvi are all missiles developed by India as part of its missile program. The Agni is a family of medium to intercontinental range ballistic missiles, the Trishul is a short range surface-to-air missile, and the Prithvi is a tactical surface-to-surface short-range ballistic missile. However, the Arjun is actually a main battle tank developed by India, not a missile.