Assertion : The magnitude of charge density for a given ligand increases as the charge on the metal

ion increases.

Reason : ${\mathrm{NH}}_{3}$ is a weak field ligand towards ${\mathrm{Co}}^{2+}$ but acts as a strong field ligand towards ${\mathrm{Co}}^{3+}.$

1. If both the assertion and the reason are true and the reason is a correct explanation of the assertion
2. If both the assertion and reason are true but the reason is not a correct explanation of the assertion
3. If the assertion is true but the reason is false
4. If both the assertion and reason are false