Assertion: Transition metal compounds are mostly paramagnetic in nature.

Reason: The paramagnetic nature increases with increase in number of unpaired electrons.

Assertion and Reason both are correct statements and reason is the correct explanation for assertion.

Transition metal compounds are mostly paramagnetic in nature due to presence of one or more unpaired electrons in their atomic orbitals.

The magnetic moment is related to the number of unpaired electrons as:

u = \(\sqrt {n(n+2)}\) where n is the number of electrons.