What is the equivalent mass of ${\text{Mn}}{{\text{O}}_{\text{2}}}$ in the present titration?
a. $\dfrac{{{\text{M}}{\text{W}}}}{{\text{1}}}$
b. $\dfrac{{{\text{M}}{\text{W}}}}{2}$
c. $\dfrac{{{\text{M}}{\text{W}}}}{3}$
d. $\dfrac{2}{3}{\text{M}}{\text{W}}$

Hint: As we know in a chemical reaction, equivalence of a substance is explained as the amount of which combines with 1 mole of hydrogen atoms or replaces the same number of hydrogen atoms. Thus equivalent weight in grams is weight in grams of 1 equivalent.

Complete step by step answer:
We know that given titration takes place in an acidic medium. Thus we can write the reaction of ${\text{Mn}}{{\text{O}}_{\text{2}}}$ is as follows:
     ${\text{M}}{{\text{n}}^{{\text{4 + }}}} + 2{e^ - } \to {\text{M}}{{\text{n}}^{2 + }}$

In the above reaction, oxidation number of Mn decreases from 4 to 2 [4-2=2]. Therefore the change in oxidation number of Mn is 2.
Now we calculate equivalent weight is as follows:
     $
  {\text{Equivalent}}\,{\text{weght = }}\dfrac{{{\text{Molecular}}\,{\text{weight}}}}{{{\text{Change}}\,{\text{in}}\,{\text{oxidation}}\,{\text{number}}}} \\
   = \dfrac{{{\text{M}}{\text{W}}}}{{\text{2}}} \\
 $

Hence option B is the correct answer.

Additional Information: We know that the law of equivalence is one equivalence of an element combined with one equivalent of others. Equivalent weight of an acid in an acid base neutralization reaction is the portion of weight of 1 mole of the acid that can furnish 1 mole of hydrogen ion and equivalent weight of a base is part of weight of one mole of base that can furnish 1 mole of hydroxide ion or accept 1 mole of hydrogen ion.

Note:
As we know for an acid titration is a procedure of quantitative analysis to determine the concentration of an acid by accurately neutralizing it with a standard solution of a base or acid that has known concentration. Generally we use titration in the food industry.