Which sample at stp has the same number of molecules as 5 liters of no2(g) at stp?
(1) 5 grams of h2(g)
(2) 5 liters of ch4(g)
(3) 5 moles of o2(g)
(4) 5 × 1023 molecules of co2(g)

(2) is the only correct answer. (1) 5 grams of H2 is 2.5 mols of this gas, which would result at STP 22.4 * 2.5 Liters (according to Avogadro's law). 5 moles of O2 would result in 5 * 22.4 Liters, and (4) 5 * 10^23 molecules of CO2 (which is what I assume you meant) would be 5 mols, which would result in 5* 22.4 Liters.

(2) is your answer

Answer is to avoid experimental error