At stp, which sample contains twice the number of molecules found in 4.00 l of hydrogen gas?

             8 L of any gas.

Explanation:
                   As we know that 1 mole of any gas at standard temperature and pressure occupies 22.4 L volume. So, 4 L of any gas will contain exactly the same number of particles as that 4 L of hydrogen gas contain. So, if you are required to double the number of particles you will have to double the volume of the gas. Therefore, 8 L of any gas will contain particles twice in number as that contained by 4 L of hydrogen gas.