The average kinetic energy \( E \) of a gas is related to its temperature and volume. The relationship between pressure and volume can be derived from the kinetic theory of gases, and for an ideal gas, it is given by:
\[
P = \frac{2E}{3V}
\]
Thus, the correct relation is:
\[
\boxed{P = \frac{2E}{3V}}
\]