Which of the following is the correct order for the theoretical magnetic moment?

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.

The aqueous solution containing which one of the following ions will be colourless?

Among the following components of cement,which is present in the highest amount?

The electronic configuration of a metal element is given below:
$M = 1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10} 4s^1$
To which block does this element belong?

Which pair of metal ions from the following has the same number of unpaired electrons?