The P-T. diagram for He, O₂, and NH₃ gas sample for adiabatic process is given. Which of the three curves corresponds to He.
 

 

For adiabatic process ${\mathrm{T}}^{\mathrm{\gamma }}{\mathrm{P}}^{1-\mathrm{\gamma }}= \mathrm{constant}$
$\therefore \frac{\mathrm{dP}}{\mathrm{dT}}=\frac{\mathrm{\gamma }}{\mathrm{\gamma }-1}\frac{\mathrm{P}}{\mathrm{T}}$

$$\begin{gathered} \mathrm{slope} \mathrm{increases} \mathrm{when} \mathrm{\gamma } \mathrm{decreases} \mathrm{and} \mathrm{vice}-\mathrm{versa}. \\ \text{'}\mathrm{He}\text{'} \mathrm{has} \mathrm{maximum} \mathrm{\gamma } \mathrm{so} \mathrm{slope} \mathrm{for} \text{'}\mathrm{He}\text{'}\mathrm{will} \mathrm{be} \mathrm{minimum} \end{gathered}$$