Which of the following represents the order of stability of ions ?

a. ${\mathrm{Cu}}^{+}>{\mathrm{Cu}}^{2+} (\mathrm{Gas} \mathrm{Phase})$
b. ${\mathrm{Cr}}^{2+}>{\mathrm{Cr}}^{3+}(\mathrm{Gas} \mathrm{Phase})$
c. ${\mathrm{V}}^{3+}>{\mathrm{V}}^{2+} (\mathrm{Gas} \mathrm{Phase})$
d. ${\mathrm{Fe}}^{2+}>{\mathrm{Fe}}^{3+} \left(\text{While bonded to a strong field ligand in an octahedral complex}\right)$

A solution of ${\mathrm{KMnO}}_4$ is reduced to various products depending upon its $\mathrm{pH}$.

• At $\mathrm{pH}<7$, it is reduced to a colourless solution ($\mathrm{A}$).
• At $\mathrm{pH}=7$, it forms a brown precipitate ($\mathrm{B}$).
• At $\mathrm{pH}>7$, it gives a green solution ($\mathrm{C}$).

Then $\mathrm{A}, \mathrm{B}$ and $\mathrm{C}$, respectively are

${\mathrm{Cr}}_2{\mathrm{O}}_7^{2-} \underset{\mathrm{Y}}{\overset{\mathrm{X}}{\rightleftarrows }} 2{\mathrm{CrO}}_4^{2-}$

$\mathrm{X}$ and $\mathrm{Y}$ are

${\mathrm{FeCr}}_2{\mathrm{O}}_4+{\mathrm{Na}}_2{\mathrm{CO}}_3+{\mathrm{O}}_2 \stackrel{\mathrm{Fusion}}{\to } \left[\mathrm{X}\right] \underset{{\mathrm{H}}_2\mathrm{O}}{\overset{{\mathrm{H}}^{+}}{\to }} \left[\mathrm{Y}\right] \underset{{\mathrm{H}}^{+}}{\overset{{\mathrm{H}}_2{\mathrm{O}}_2}{\to }} \left[\mathrm{Z}\right]$

Which of the following statements is true for the compounds $\left[\mathrm{X}\right], \left[\mathrm{Y}\right]$ and $\left[\mathrm{Z}\right]$?

Which of the following represents the incorrect order of property mentioned?