Give methods of preparation for benzene.

(N/A) Industrially,benzene is prepared from coal tar. In laboratory,it is prepared by the following methods:
$(i)$ Cyclic polymerisation of ethyne: $3CH \equiv CH \xrightarrow{\text{Red hot iron tube}, 873 \ K} C_6H_6$ (Benzene)
(ii) Cyclisation of $n$-hexane: $n-C_6H_{14} \xrightarrow{Cr_2O_3/V_2O_5/Mo_2O_3, 773 \ K, 10-20 \ atm} C_6H_6 + 4H_2$
(iii) Decarboxylation of benzoic acid: Sodium benzoate on heating with soda lime $(NaOH + CaO)$ gives benzene: $C_6H_5COONa + NaOH \xrightarrow{\Delta} C_6H_6 + Na_2CO_3$
(iv) Reduction of phenol: Phenol is reduced to benzene by passing its vapours over heated zinc dust: $C_6H_5OH + Zn \xrightarrow{\Delta} C_6H_6 + ZnO$