What is the total number of nitrogen atoms in 0.25 mole of no2 gas?

Avogadro's number represents the number of units in one mole of any substance. This has the value of 6.022 x 10^23 units / mole. This number can be used to convert the number of atoms or molecules into number of moles.

0.25 mol NO2 (1 mol N / 1 NO2) (6.022 x 10^23 atoms / mol) = 1.5055x10^23 atoms