Transition elements form complex compounds due to:

Many transition metals form interstitial compounds. The characteristics of these interstitial compounds are:
$I$. They have high melting points,higher than those of pure metals.
$II$. They are very hard.
$III$. They retain metallic conductivity.
$IV$. They are chemically more reactive than the pure metals.

Which of the following has the maximum number of unpaired electrons?

General electronic configuration of outermost and penultimate shell is $(n - 1)s^2 (n - 1)p^6 (n - 1)d^x ns^2$. If $n = 4$ and $x = 5$,then the number of protons in the nucleus will be:

What should be the difference in atomic radii of metals to form an alloy?

The higher oxidation states of transition elements are found to be in combination with $A$ and $B$,which are: