If you have exactly 2.00 moles each, of two different substances, then which of the following must be true about the two samples?

The true is that both substances will have 2 * 6.02* 10^23 = 12.04 * 10^23 particles (may be molucules or atoms(.

Also, the two moles of each substance will have different masses, because you have to multiply the number of moles of each substance by the respective molar mass (or atomic mass).