Suppose 10 atoms of carbon react with 20 atoms of oxygen to form 10 molecules of carbon dioxide according to the law of conservation of mass how many atoms are present in this reaction

In the reaction, each molecule of carbon dioxide contains one atom of carbon and two atoms of oxygen. So, 10 molecules of carbon dioxide would contain 10 atoms of carbon and 20 atoms of oxygen. Therefore, in this reaction, there are 10 + 20 = <<10+20=30>>30 atoms present.