An atom with atomic number $21$ belongs to the category of

Elements which generally exhibit multiple oxidation states and whose ions are usually coloured are

Which of the following transition metals has the lowest density?

$A$ substance contains an $M^{3+}$ ion with the electronic configuration $[Ar]3d^1$. The ion is........

Invar,an alloy of $Fe$ and $Ni$,is used in watches and meter scales. Its characteristic property is:

The magnetic moment of $M^{x+}$ (atomic number $= 25$) is $\sqrt{15} \ BM$. The number of unpaired electrons and the value of $x$,respectively,are