Who one of the following had not come to India with Alexander?

The correct answer is C, Deimachus. He is the odd one out because he was not part of Alexander's campaign at all. Deimachus was an envoy sent by Seleucus I Nicator to the Mauryan court of Bindusara at Pataliputra, around 298 to 272 BCE, well after Alexander had left India in 325 BCE.

• Nearchus (A): Alexander's admiral, who commanded the fleet that sailed from the Indus delta to the Persian Gulf around 326 to 325 BCE.
• Onesicritus (B): Chief pilot of Alexander's fleet, who accompanied the king in India and later wrote an account of the campaign.
• Aristobulus (D): A military engineer and historian who accompanied Alexander's army, and whose memoir was later used by Arrian.

The core concept here is the Indo-Greek contact that followed the campaign. Seleucid diplomacy with the Mauryas produced Megasthenes' Indica and Deimachus' mission, which are key sources for Mauryan administration and society, a frequent Mains theme.

Trap: Candidates often pick the person who sounds least familiar, assuming the best-known figures are all from Alexander's campaign. Check the dates. Deimachus belongs to the Seleucid–Mauryan period, not the Macedonian invasion.