Question

How many moles of o2 are present in 1litre of air at ntp?

Answer 1

1 litre of air contains 80%  by volume. So is 0.8 L.

At STP, 1 mole of  occupies 22.4 L. Hence , we can find how many moles occupy 0.8 L by  .

1 mole contains avagadro number() of particles. So, 0.0357 moles contains  molecules