Two moles of oxygen gas is heated at constant pressure from 25°C to 75°C. The increase in internal energy of the gas in terms of gas constant R is

• A

  $\frac{100R}{\mathrm{\gamma }-1} \mathrm{joule}$

• B

  $\frac{75\mathrm{\gamma R}}{\mathrm{\gamma }-1} \mathrm{joule}$

• C

  $\frac{25\mathrm{R}}{\mathrm{\gamma }-1} \mathrm{joule}$

• D

  $\frac{75\mathrm{R}}{\mathrm{\gamma }-1} \mathrm{joule}$