Amongst  $Ti{F_6}^{2 - }\,,\,Co{F_6}^{3 - }\,,\,C{u_2}C{l_2}$ and $NiCl_4^{2-}$ the colourless species are 

Which is not true for transition elements

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 melting point of $Zn$ is lower as compared to those of the other elements of $3d$ series because

Which of the following pair of elements cannot form an alloy

Mercury is transported in metal containers made of