The correct answer is (d). A constitutional government is a government that is limited by the terms of the Constitution. This means that the government’s powers are defined and limited by the Constitution, and the government cannot act outside of those limits.
Option (a) is incorrect because a representative government of nation with federal structure is not necessarily a constitutional government. For example, the United States is a representative government of nation with federal structure, but it is also a constitutional government.
Option (b) is incorrect because a government whose Head enjoys nominal powers is not necessarily a constitutional government. For example, the United Kingdom is a government whose Head enjoys nominal powers, but it is not a constitutional government.
Option (c) is incorrect because a government whose Head enjoys real powers is not necessarily a constitutional government. For example, North Korea is a government whose Head enjoys real powers, but it is not a constitutional government.