Which of the following has maximum first ionisation energy ?

Why $E^o$ values for $Mn,\,Ni$ and $Zn$ are more negative than expected ?

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

Which of the following transition metal is used as a catalyst

Among $TiF^{2-}_6 ,CoF^{3-}_6 ,Cu_2Cl_2$ and $NiCl^{2-}_4$ the colourless species  are