the total mass of 1.81 x10^24 particle nitrogen gas is calculated as follows
find the moles of nitrogen
1 moles = 6.022 x10 ^23 particles
what about 1.81 x10^23 =? moles
= (1.81 x10^ 24)/(6.022 x10^23) = 3 moles
mass = moles x molar mass of nitrogen gas = 14 x2 = 28 g/mol
= 3 moles x28 g/mol = 84 grams