The correct option is B a system of government in which the power is divided between a central authority and constituent political units.
Federalism is a system of government in which the power is divided between a central authority and various constituent units of the country. Usually, a federation has two levels of government. One is the government for the entire country that is usually responsible for a few subjects of common national interest. The others are governments at the level of provinces or states that look after much of the day-to-day administering of their state.