$Cr _2 O _7^{2-}+ XH ^{+}+6 Fe ^{2+} \rightarrow YCr ^{3+}+6 Fe ^{3+}+ ZH _2 O$
$X , Y$ અને $Z$ નો સરવાળો $......$ છે.
$x =14$
$y =2$
$z =7$
Hence $(x+y+z)=14+2+7=23$
$C + {O_2} \to C{O_2};\Delta H = - 393\,J$
$2Zn + {O_2} \to 2ZnO;\Delta H = - 412\,J$
${N_2} + 3{H_2} \longrightarrow NH_3$
${H_2}O + B{r_2} \to HOBr + HBr$