${\rm{F}}{{\rm{e}}^{3 + }}$

${\rm{C}}{{\rm{r}}^{3 + }}$

${\rm{C}}{{\rm{u}}^{2 + }}$

${\rm{C}}{{\rm{u}}^ + }$

$Cr^{3+} \rightarrow Cr^{2+}$

$Fe^{3+} \rightarrow Fe^{2+}$

$Mn^{3+} \rightarrow Mn^{2+}$

$Co^{3+} \rightarrow Co^{2+}$

German silver

Beryllium bronze

Constantan

Fool’s gold

They show variable oxidation states.

Their compounds are often colored.

They often exhibit catalytic activity.

They have completely filled d subshells in all their oxidation states.

${\rm{ZnC}}{{\rm{l}}_2}$

${\rm{Zn}}{\left( {{\rm{N}}{{\rm{O}}_3}} \right)_2}$

${\left( {{\rm{C}}{{\rm{H}}_3}{\rm{COO}}} \right)_2}{\rm{Zn\;}}$

None of these

Zero

4

3

1

${\rm{HgO}}$

${\rm{H}}{{\rm{g}}_2}{\rm{O}}$

${\rm{N}}{{\rm{H}}_2}-{\rm{Hg}}-{\rm{Hg}}-{\rm{Cl}}$

${\rm{HgN}}{{\rm{H}}_2}{\rm{Cl}}$

Ammonia soda process ⎯ manufacture of potassium carbonate

Bessemer’s process ⎯ manufacture of steel

Mac Arthur and Forest process ⎯ extraction of silver

Dow’s process ⎯ manufacture of phenol

MnO₃

CrO₃

FeO₃

TiO₃

Lead oxide

Copper oxide

Sodium oxide

Manganese dioxide

Manufacture of blue-black ink

Manufacture of chalks

Preparation of hydrogen sulphide

Preparation of sulphur dioxide