(A) is true, (R) is true and (R) is the correct explanation for (A).

(A) is true, (R) is true but (R) is not the correct explanation for (A).

(A) is true but (R) is false.

(A) is false but (R) is true.

more the charge on the atom, more is its stability.

electronic configuration of $\mathrm{Fe}^{2+}$ is $3 d^6$ while that of $\mathrm{Fe}^{3+}$ is $3 d^5$.

$\mathrm{Fe}^{2+}$ has a larger size than that of $\mathrm{Fe}^{3+}$.

$\mathrm{Fe}^{3+}$ ions are coloured.

$\mathrm{Cu}, \mathrm{Ni}, \mathrm{Zn}$

$\mathrm{Ni}, \mathrm{Au}, \mathrm{Cd}$

$\mathrm{Au}, \mathrm{Hg}, \mathrm{Pd}$

$\mathrm{Zn}, \mathrm{Cd}, \mathrm{Hg}$