A constitutional government by definition is a

A constitutional government is one whose powers are defined and restricted by a constitution, a higher law that binds rulers as well as the ruled. That makes it a limited government, so option D is correct.

• A (government by legislature): Legislative control describes parliamentary or legislative supremacy, not constitutionalism. Britain has no single written constitution yet is still broadly constitutional, so legislative control is not the defining feature.
• B (popular government): Popular government means rule by the people, which is democracy. A constitutional government may be democratic, but a monarchy bound by a constitution is also constitutional. Popularity is not the definition.
• C (multi-party government): Multi-party or coalition arrangements are features of the party system. They say nothing about restraints on state power.

The core concept is constitutionalism: power is checked by fundamental law, rights and separation of powers. Article 13, which makes laws inconsistent with Fundamental Rights void, is a working example. For Mains, this links to judicial review and the basic structure doctrine in Kesavananda Bharati (1973).

Trap: Aspirants pick B because constitutional and democratic feel interchangeable. Constitutionalism is about limits on power, while democracy is about the source of power.