આપેલ : $2 Cu ^{2+}+4 I ^{-} \rightarrow Cu _{2} I _{2}+ I _{2}$
$I _{2}+2 S _{2} O _{3}{ }^{2-} \rightarrow 2 I ^{-}+ S _{4} O _{6}{ }^{2-}$
$2 \times n _{ mol }$ of $I _{2}=0.4$
$n _{ mol }$ of $I _{2}=0.2 m mol$
$n _{ mol }$ of $Cu ^{+2}=0.2 \times 2 \times 10^{-3}$
$\left[ Cu ^{+2}\right]=\frac{0.4 \times 10^{-3}}{10 \times 10^{-3}}=0.04=4 \times 10^{-2}$
$S _{8( s )}+ a OH ^{-}_{( aq )} \rightarrow b S ^{2-}_{( aq )}+ c S _{2} O _{3}{ }^{2-}{ }_{( aq )}+ d H _{2} O _{(\ell)}$
$'a'$ નું મૂલ્ય ............ છે. (પૂર્ણાક જવાબ)