# The main reason d-block elements exhibit a large number of oxidation states compared to f-block elements is because:

(1) There are more d-block elements (2) The difference in the energy of (n-1) d orbital and ns orbital is very small (3) The d-block elements have smaller atomic numbers compared to f-block (4) None of the above

Answer: The difference in the energy of (n-1) d orbital and ns orbital is very small
Given that both sub-shells are available depending upon the number of d electrons involved in bonding, diferent oxidation states arise.
However, in f-block, (n-2)f orbitals are not available for bonding.
edited Aug 4, 2014