Explain the following :

The colour of ${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$ solution changes with the change in $\mathrm{pH}$ value of the solution.

Assign reasons for the following:

${\mathrm{Zn}}^{2+}$ salts are white while ${\mathrm{Cu}}^{2+}$ salts are blue.

Assign reasons for the following:

Assign reasons for the following:

${\mathrm{Co}}^{2+}$ has higher magnetic moment than ${\mathrm{Ni}}^{2+}$

Assign reasons for the following:

The ionization enthalpies of $5\mathrm{d}$ elements are greater than $3\mathrm{d}$ elements.

Assign reasons for the following:

Write equations for the preparation of ${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$ from chromite ore.

Assign reason for the following :

${\mathrm{Sc}}^{3+}$ ion is colourless while ${\mathrm{Cr}}^{3+}$ is coloured.

Assign reasons for the following :

${\mathrm{Mn}}^{2+}$ compounds are more stable than ${\mathrm{Fe}}^{2+}$ compounds towards oxidation to $+3$ state.

Assign reasons for the following :

$\mathrm{Cu}\left(\mathrm{I}\right)$ compounds are white and diamagnetic while $\mathrm{Cu}\left(\mathrm{II}\right)$ compounds are coloured and paramagnetic.