Who among the following can join the National Pension System (NPS)?

The correct answer is C. NPS membership for state government employees is not automatic. Each state decides whether and from when to adopt NPS through its own notification, so only those joining after that date are covered. This is a federal-structure point under Polity and Governance, and it is a recurring theme in discussions of pension reform and the fiscal burden of the old pension scheme.

• A is wrong: NPS is not limited to resident citizens. Non-resident Indians have been allowed to join since 2009, so the restriction in A does not hold.
• B is wrong: There is no fixed 21 to 55 age bar. Entry is open from age 18, with upper limits that have changed over time and exit norms revised later.
• D is wrong: The central government mandate applied to employees joining from 1 January 2004, not 1 April 2004. Armed Forces personnel were brought under NPS through a separate later notification, so the statement as written is inaccurate.

Trap: Candidates often treat D as correct because it looks like the cleanest, most complete statement. The date and the Armed Forces detail are where it fails.