• Which has more number of atoms? 100g of N2 or 100g of NH₃

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Number of moles is determine by the formulae :-
n = given mass/ molar mass
Where n stands for number of moles 
given mass for both case is 100 g
Molecular mass of N₂ is (14 + 14) = 28 g per mole
Molecular mass of NH₃ is {14 +(3$\times$1)} = 17 g per mole
As Atomic mass of Nitrogen is 14 and atomic mass for hydrogen is 1 g per mole.
1. number of mole of N₂ = 100/ 28 = 3.57 mole
As 1 molecule of dinitrogen contain 2 atoms, 
Therefore number of atoms present in 3.57 mole of nitrogen is 
3.57 $\times$2
= 7.14 mole
2. Number of mole of NH₃ = 100/17
= 5.88
As 1 molecule of ammonia contain = 3 atoms
Therefore, 
5.88 moles of ammonia contain = 3 $\times$ 5.88
= 17.65 atoms
Hence 100g of ammonia contain more number of atoms.