In the chemical reactions given above A and B respectively are:

$$\mathrm{ArN_2^+Cl^- + H_3PO_2 + H_2O \rightarrow ArH + N_2 + H_3PO_3 + HCl}$$ (From Amines chapter in NCERT).

$$\mathrm{C_6H_6 + CH_3Cl \xrightarrow[\ ]{Anhyd.\ AlCl_3} C_6H_5CH_3 + HCl}$$ (From Hydrocarbons chapter in NCERT, Friedel-Crafts Alkylation Reaction)
Similarly if we use $$ CH_3CH_2Cl$$

$$\mathrm{C_6H_6 + CH_3CH_2Cl \xrightarrow[\ ]{Anhyd.\ AlCl_3} C_6H_5CH_2CH_3 + HCl}$$

Thus the right option is A.