Which forms coloured salts?

Discuss the magnetic properties of transition elements.

Which among the following elements does not have any electron in the $f-$subshell in either its expected or observed electronic configuration?

The placement of $Zn,$ $Cd,$ and $Hg$ along with $d-$block elements is not considered proper because:

The increase in the atomic radii of the third $(5d)$ series of transition elements is very small, which may be accounted for by the filling of '$X$' orbitals before '$Y$' orbitals. $X$ and $Y$ are:

Highest density is of $...$.