Consider the reaction, ${\mathrm{MnO}}_2+4\mathrm{HCl}\to {\mathrm{MnCl}}_2+2{\mathrm{H}}_2\mathrm{O}+{\mathrm{Cl}}_2;$ In this reaction two moles of HCl reduces ‘X’ moles of ${\mathrm{MnO}}_2$ .  Value of  ‘X’ is

${\mathrm{MnO}}_2+4\mathrm{HCl}\to {\mathrm{MnCl}}_2+2{\mathrm{H}}_2\mathrm{O}+{\mathrm{Cl}}_2;$ 1 mole of ${\mathrm{MnO}}_2$ reacts with 4 moles of HCl;

 Of the 4 moles of HCl, only two moles are oxidized to ${\mathrm{Cl}}_2$ by one mole of ${\mathrm{MnO}}_2$

Alternate method: 

Criss-cross :

1 mole of ${\mathrm{MnO}}_2$ oxidizes 2 moles of HCl