The number of unpaired electrons in $Mn^{3+}$ is

In the $3d$ transition series,as the atomic number increases,the paramagnetic character:

Which of the following statements are correct about $Zn$,$Cd$ and $Hg$?
$(I)$ They exhibit high enthalpies of atomisation as the $d-$subshell is full.
$(II)$ $Zn$ and $Cd$ do not show variable oxidation states while $Hg$ shows $+I$ and $+II$.
$(III)$ Compounds of $Zn$,$Cd$ and $Hg$ are paramagnetic in nature.
$(IV)$ $Zn$,$Cd$ and $Hg$ are called soft metals.

What are the characteristics of the transition elements and why are they called transition elements? Which of the $d$-block elements may not be regarded as the transition elements?

Which of the following pairs of elements have one electron in the $5d$-subshell in their observed electronic configuration?

Which of the following ions is most stable in aqueous solution?