(a) The number of atoms or molecules in 12 gm of carbon-12 ( in a mole of a substance) is called as Avogadro constant (6.022 × 1023 )
(b) Number of molecules(N) = Given mass X Avgadros no / Molar mass
Molar mass of 1 mole of N2= 14 × 2 =28
N = 56/ 28 ×6.022 × 1023
N = 12.044 × 1023
Hence there are 12.044 × 1023 particles present in 56 gm of N2