a
Given process is isobaric.
$\therefore \,dQ = n{C_p}dT;\,where\,{C_p}\,is\,specific\,heat\,at\,constant\,pressure.$
or $dQ = n\left( {\frac{5}{2}R} \right)dT$
$Also,\,dW = PdV = nRdT\,\left( {PV = nRT} \right)$
Required ratio$ = \frac{{dW}}{{dQ}} = \frac{{nRdT}}{{n\left( {\frac{5}{2}R} \right)dT}} = \frac{2}{5}$