Which element from the following in $+3$ oxidation state forms colourless compounds?

Illustrate by taking examples of transition elements and non-transition elements that oxidation states of elements are largely based on electronic configuration.

The spin-only magnetic moment value of $M^{3+}$ ion (in gaseous state) from the pairs $Cr^{3+}/Cr^{2+}$,$Mn^{3+}/Mn^{2+}$,$Fe^{3+}/Fe^{2+}$,and $Co^{3+}/Co^{2+}$ that has a negative standard electrode potential,is $B.M.$ (Nearest integer).

Interstitial compounds are formed by

Which among the following elements does $NOT$ exhibit ferromagnetic properties?

Compare the stability of the $+2$ oxidation state for the elements of the first transition series.