Which of the following is a diamagnetic transition metal ion?

The element which shows only one oxidation state other than its elemental form is:

Explain giving reasons:
$(i)$ Transition metals and many of their compounds show paramagnetic behaviour.
$(ii)$ The enthalpies of atomisation of the transition metals are high.
$(iii)$ The transition metals generally form coloured compounds.
$(iv)$ Transition metals and their many compounds act as good catalysts.

Among the following transition elements,which one has the lowest first ionization energy?

The electronic configuration of $Cr^{3+}$ is

Which of the following mixtures can form an alloy?