Which of the following is a soft metal?

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).

The general electronic configuration of the transition elements is

Which transition series includes elements $Co$ and $Mo$ respectively?

In which of the following ions,$d-d$ transition is not possible?

The element with which of the following outer electron configuration may exhibit the largest number of oxidation states in its compounds?