Q. In an ideal gas, which of the following is true at the same temperature?
✅ Correct Answer: (B)
All gases have the same average kinetic energy per molecule.
Explanation: At a given temperature, the average translational kinetic energy per molecule depends only on temperature: (1/2)mv^2_avg ∝ kT. Different gases have different molar masses and densities, so options 1 and 3 are false. Option 4 is false because number of molecules in a given volume depends on pressure and temperature; at the same T and P equal volumes contain same number of moles (Avogadro's law) but the statement lacked pressure and is ambiguous — moreover molar masses differ so mass density changes.
Explanation by: Sikhar Chaudhary
At a given temperature, the average translational kinetic energy per molecule depends only on temperature: (1/2)mv^2_avg ∝ kT. Different gases have different molar masses and densities, so options 1 and 3 are false. Option 4 is false because number of molecules in a given volume depends on pressure and temperature; at the same T and P equal volumes contain same number of moles (Avogadro's law) but the statement lacked pressure and is ambiguous — moreover molar masses differ so mass density changes.