First, we assume that helium behaves as an ideal gas such that the ideal gas law is applicable.
PV = nRT
where P is pressure, V is volume, n is number of moles, R is universal gas constant, and T is temperature. From the equation, if n, R, and T are constant, there is an inverse relationship between P and V. From the given choices, the container with the greatest pressure would be the 50 mL.