Answer:
b. Only II is correct
Explanation:
Remember that STP means that the temperature is 273 K and the pressure is 101.3 KPa.
Density is an intensive property, that mean that does not depend on the quantity of substance, so if you have 1 mole or 2 is the same. Density of N2 is 1.25 g/L.
The mass of 1 mole of N2 is 28 g, but in this case you have 2 moles, that means the double of grams, that is the reason, why is incorrect this option.