The inalienable attribute of the parliamentary system of government is the fusion of executive and legislature. This means that the executive branch, which includes the prime minister and the cabinet, is also a part of the legislative branch, which is the parliament. In a parliamentary system, the executive is responsible to the legislature and can be dismissed by a vote of no confidence. This fusion of power ensures a close relationship between the executive and legislative branches, leading to efficient decision-making and accountability. Option 1, flexibility of the constitution, is not an inalienable attribute of the parliamentary system, as the flexibility of the constitution can vary in different parliamentary systems. Option 3, judicial supremacy, and option 4, parliamentary sovereignty, do not define the parliamentary system, but rather describe different forms of government.