Write about the utility of $d$- and $f$-block elements and their compounds. Or describe the following uses of $d$- and $f$-block elements and their compounds: $(i)$ In iron/steel $(ii)$ As pigments $(iii)$ In batteries $(iv)$ In coinage $(v)$ As catalysts.

(A) $(i)$ Production and use of iron and steel: Iron and steel are important construction materials. Their production is based on the reduction of iron oxide compounds,removal of impurities,and the addition of carbon and alloying metals like $Cr$,$Mn$,and $Ni$.
$(ii)$ In pigment industry: $TiO_2$ is produced for the pigment industry.
$(iii)$ In battery industry: The following are produced for the battery industry:
$\Rightarrow MnO_2$ and $Zn$ for dry cells.
$\Rightarrow Ni/Cd$ for batteries.
$(iv)$ In coinage: Group $11$ elements are valuable and are known as coinage metals. The importance of $Ag$ and $Au$ is limited to storage,but they have industrial uses. In the $UK$,'copper coins' are steel coated with copper,and 'silver coins' are $Cu/Ni$ alloys.
$(v)$ As catalysts: Many elements or their compounds are essential catalysts for chemical industries.
$\Rightarrow V_2O_5$ is used as a catalyst for the oxidation of $SO_2$ to $SO_3$ in the production of sulfuric acid.
$\Rightarrow$ Ziegler-Natta catalyst,which is $TiCl_4$ with $Al(CH_3)_3$,is used in the production of polyethylene.
$\Rightarrow$ Iron catalysts are used in the Haber process for the production of ammonia from $N_2/H_2$ mixtures.
$\Rightarrow$ Nickel acts as a catalyst in the hydrogenation of fats (unsaturated oils).
$\Rightarrow PdCl_2$ is used as a catalyst for the oxidation of ethyne $(C_2H_2)$ in the Wacker process to produce ethanal $(CH_3CHO)$.
$\Rightarrow$ Nickel complexes are used in the polymerization of alkynes and other organic compounds like benzene.
$\Rightarrow$ The photography industry is based on the special light-sensitive properties of $AgBr$.