For an ideal gas, the correct statement that does not hold true is option 1: "The speed of all gas molecules is the same."

In an ideal gas, the gas molecules are considered to be point particles with negligible volume and no intermolecular forces. However, the kinetic theory of gases states that gas molecules have a range of speeds. This means that the velocities of the gas molecules in an ideal gas are not all the same. Some gas molecules will have higher velocities, while others will have lower velocities. Consequently, the statement that the speed of all gas molecules is the same is not applicable to an ideal gas.

Option 2 is correct because the kinetic energies of the gas molecules in an ideal gas are not all the same. Kinetic energy is directly proportional to the square of the velocity, so molecules with higher speeds will have higher kinetic energies.

Option 3 is correct because the potential energy of gas molecules in an ideal gas is considered to be zero since there are no intermolecular forces.

Option 4 is correct because ideal gases are assumed to have no interactive forces between the gas molecules.

In summary, the statement that does not hold true for an ideal gas is that the speed of all gas molecules is the same.