b
\(Zn\,\, + \,\,2HCl\,\, \to \,\,ZnC{l_2}\, + \,\,{H_2}  \)
\(\,\,\,\,\,\,\,\,\,\,1\,mol\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,1\,mol  \) 

\(H_2\) વાયુનું કદ 

\( {{\text{V}}_{{{\text{H}}_{\text{2}}}}}\, = \,\,\frac{{{\text{nRT}}}}{{\text{P}}}  \) 
\({{\text{V}}_{{{\text{H}}_{\text{2}}}}}\, = \,\,\frac{{{\text{1}}\,\, \times \,\,{\text{0}}{\text{.821}}\,\, \times \,\,{\text{300}}}}{{\text{1}}}{\text{ }}\, = \,\,\,24.63\,\,lit. \)
 \( W\,\, = \,\, - \,P\Delta V\, \cong \,\, - \,P{V_{{H_2}}}\, = \,\, - \,24.63\,\,\,\,\,\,L\, - \,atm  \) 
 \( \therefore \,\,W\,\, = \,\, - \,2495\,J \)