\(X\) મોલની સંખ્યા \( = \frac{{1.65 \times {{10}^{21}}}}{{{N_A}}}\)

\(\therefore \,\,\,{\text{X}}\) નું વજન \( = \frac{{1.65 \times {{10}^{21}}}}{{{N_A}}} \times m\,\,gm\)

\(Y\,\) મોલની  સંખ્યા \( = \frac{{1.85 \times {{10}^{21}}}}{{{N_A}}}\)

\(\therefore \,\,Y\) નું વજન \( = {\text{ }}\frac{{{\text{1}}{\text{.85}} \times {\text{1}}{{\text{0}}^{{\text{21}}}}}}{{{N_A}}} \times 187\,gm\)

આપેલ \(X\) નું વજન \(+ Y\) નું વજન \(= 0.688\) ગ્રામ

\(\therefore \,\,\frac{{1.65 \times {{10}^{21}} \times m}}{{{N_A}}} + \frac{{1.85 \times {{10}^{21}} \times 187}}{{{N_A}}}\,\, = \,\,0.688\)

\(\therefore \,\,\,\,m = 42\)