B) 126 J
Explanations:
\(Q_p=\mu C_p\Delta T \,and\, Q_v = \mu C_v\Delta T\)
\(\Rightarrow \frac{QV}{Qp}=\frac{CV}{CP}=\frac{\frac{3}{2}R}{\frac{5}{2}R}=\frac{3}{5}\)
\([\therefore(CV)_{mono}=\frac{3}{2}R,(C_p)_{mono}=\frac{5}{2}R]\)
\(\Rightarrow QV=\frac{3}{5}\)\(\times(\Delta Q)P\)
\(=\frac{3}{5}\times210 = 126J\)