Which of the following ions will exhibit colour in aqueous solution?

For $M^{2+} / M$ and $M^{3+} / M^{2+}$ systems,the ${E^{\Theta}}$ values for some metals are as follows:
$Cr^{2+} / Cr : -0.9 \ V$
$Cr^{3+} / Cr^{2+} : -0.4 \ V$
$Mn^{2+} / Mn : -1.2 \ V$
$Mn^{3+} / Mn^{2+} : +1.5 \ V$
$Fe^{2+} / Fe : -0.4 \ V$
$Fe^{3+} / Fe^{2+} : +0.8 \ V$
Use this data to comment upon:
$(i)$ The stability of $Fe^{3+}$ in acid solution as compared to that of $Cr^{3+}$ or $Mn^{3+}$ and
$(ii)$ The ease with which iron can be oxidised as compared to a similar process for either chromium or manganese metal.

Which of the following pairs of substances exhibit paramagnetism among $K_2SO_4$,$MgCl_2$,$FeSO_4$,$NiCl_2$,and $ZnO$?

Which of the following series of transition elements has the general electronic configuration $[Kr] 4d^{1-10} 5s^{0-2}$?

Discuss the magnetic properties of transition elements.

Find the correct order of the given elements with respect to their size.