Which of the following ions are paramagnetic and coloured?

The correct order of density for the $3d$ series elements is:

The correct order of spin-only magnetic moment (in $BM$) for $Mn^{2+}$,$Cr^{2+}$,and $Ti^{2+}$ ions is:

Fill in the blanks:
$(a)$ The shielding effect of $d$-electrons is ......... effective than $p$-electrons.
$(b)$ $A$ decrease in exchange energy leads to a ......... in stability.
$(c)$ The maximum oxidation state of $Mn$ is ..........
$(d)$ The stability of $Mo(VI)$ and $W(VI)$ is found to be .......... than that of $Cr(VI)$.

$A$ transition element $X$ has a configuration $[Ar]3d^4$ in its $+3$ oxidation state. Its atomic number is

The lanthanide contraction is responsible for the fact that