(2C+2+N-X-H)/2
(2*7+2+0-0-8)/2
4
Isotopes are elements with the same number of protons but different number of neutrons
Potassium chloride reacts with ammonium nitrate to give ammonium chloride and potassium nitrate.
This is a type of double displacement reaction. The balanced chemical equation can be represented as,

Total ionic equation for this reaction will be,

There is no apparent reaction as this reaction is not accompanied by the formation of a gas or a solid precipitate. We cannot observe any visual reaction as there is not net reaction taking place. All the ions remain as spectator ions.
Answer:
We can say, there are 4 mol of oxygen with (4 . NA) = 2.40ₓ10²⁴ atoms
Or just, 4 atoms oxygen.
Explanation:
CH₄ + 2O₂ → CO₂ + 2H₂O
1 mol of methane reacts with 2 mol of oxygen to produce 1 mol of carbon dioxide and 2 mol of water.
We count in 1 mol of CO₂, we have 2 mol of oxygen
In 2 mol of water, we have 2 mol of oxygen.
We can say, there are 4 mol of oxygen with (4 . NA) = 2.40ₓ10²⁴ atoms
Or just, 4 atoms oxygen.