Constitutional government means

(a) a representative government of a nation with federal structure
(b) a government whose Head enjoys nominal powers
(c) a government whose Head enjoys real powers
(d) a government limited by the terms of the Constitution ✓ UPSC's answer

Why the answer is (d)

• Constitutional government (constitutionalism) means a government whose powers are defined and limited by a constitution, so that authority is exercised under law and not arbitrarily — option (d).

• Its essence is limited government: rule of law, separation of powers, fundamental rights and judicial review restrain those in power.

• It is independent of form: a constitutional government may be unitary or federal (a), and its head may hold nominal powers as in a parliamentary system (b) or real powers as in a presidential system (c).

• Even a monarchy (UK) can be a constitutional government if power is limited.

• Hence option (d).

Why the other options are wrong

(a) a representative government of a nation with federal structure: Federal structure is not required for constitutional government.
(b) a government whose Head enjoys nominal powers: A nominal head describes parliamentary form, not constitutionalism.
(c) a government whose Head enjoys real powers: A real-power head describes presidential form, not constitutionalism.

Asked in the GS Paper I of the UPSC Civil Services Preliminary Examination 2021, held on 10 October 2021. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.