Identify the outer electronic configuration of the $first$ element of the $first$ transition series.

Ferrous ion changes to $X$ ion upon reacting with acidified hydrogen peroxide. The number of $d$-electrons present in $X$ and its magnetic moment (in $BM$) are,respectively:

Identify the incorrect statement in the following.

Which of the following general configurations of the outermost shell represents the chromium element [$Cr$'s atomic number $= 24$]?

The lanthanide contraction is responsible for the fact that

Which of the following pairs of ions are colourless?