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# Chemical reactions involve interaction of atoms and molecules.A large number of atoms/molecules are present in a few grams of any chemical compound varying with their atomic/molecular masses.To handle such large numbers conveniently,the mole concept was introduced.This concept has implications in diverse areas such as analytical chemistry,biochemistry,electrochemistry and radiochemistry.The following example illustrates a typical case involving chemical/electrochemical reaction.A H.O molar aqueous solution of NaCl is prepared and 500ml of this solution is electrolysed.This leads to the evolution of chlorine gas at one of the electrodes(atomic mass:Na=23,Hg=200;1 faraday=96500 coulombs).The total number of moles of chlorine gas evolved is:

$\begin{array}{1 1}(a)\;0.5& (b)\;1.0 \\(c)\;2.0& (d)\;3.0\end{array}$

The number of moles of NaCl=Number of moles of $Cl^{-}=2$mole$(4\times \large\frac{1}{2})$
$\therefore$Number of moles of $Cl_2$ gas evolved=$\large\frac{2}{2}$=1mole$(2NaCl\rightarrow Cl_2)$
Hence (b) is the correct answer.