If we release a magnet held in our hand, it falls to the ground. The force which makes the magnet fall down is an example of:
$(a)$. balanced force
$(b)$. unbalanced force
$(c)$. magnetic force
$(d)$. muscular force

When we release a magnet held in our hand, it falls to the ground. The force which makes the magnet fall down is an example of an unbalanced force as only an unbalanced force can bring an object into motion from rest and vice-versa.

So, option (b) is correct.