Concept:A confederal state is a union of independent units in which the central government is weak and the units retain their sovereignty.
Explanation:In a confederal state, the member units are more powerful than the central authority.
The central government depends on the units for its existence and functions.
The units are not permanently bound by the constitution.
Therefore, a unit has the right to leave the union at any time.
This right is known as secession.
Hence, a key feature of a confederal state is that any unit can secede at will.
Option A is incorrect because a confederal state is not a single sovereign state.
Option B is incorrect because the constitution is often rigid, not flexible.
Option D is incorrect because powers are not shared equally between the centre and the units.
Answer:C. any unit can secede at will