Given the fact that the Reserved Powers lie within the constituent states, the specific Marriage Laws the and the Conduction of Elections are decisions taken by each state in different ways. Due to the Reserved Powers each state has the autonomy to govern itself in such matters.
In other words, Reserved powers, residual powers, or residuary powers are the powers which are neither prohibited nor openly given by law to any organ of government. Such powers, as well as general power of competence, are given because it is not practical to detail in legislation every act allowed to be carried out by the state.
So the final answer is: Reserved Powers