A Parliamentary System of Government is the one in which

The correct answer is B. The core idea of parliamentary government is that the executive is accountable to the legislature. The Council of Ministers is collectively responsible to the Lok Sabha under Article 75(3), and it stays in office only so long as it enjoys the confidence of the House. A no-confidence motion can remove it, and that is the defining feature.

• A is wrong. Every party in Parliament being in government describes an all-party or broad-based government, which is a situation and not a defining feature of the system. Opposition parties exist in a parliamentary system by design.
• C is wrong. In a parliamentary system the people elect the legislature, and the executive emerges from it indirectly. Direct election of the government and its removal by voters is a feature of some presidential or direct-election arrangements, not of parliamentary government.
• D is wrong. A head of government chosen by the legislature and irremovable before a fixed term describes a presidential-style arrangement. In a parliamentary system the government can be removed mid-term.

This concept links to the Mains question on executive-legislature relations and the Westminster model. It also helps you compare parliamentary and presidential systems in GS-II.

Trap: Aspirants often pick A because coalition governments look like "all parties in government." The test is accountability: who can remove whom.