Answer: 8 oxygen atoms and 4 hydrogen atoms. Explanation down below.
Explanation: One molecule of oxygen gas is composed of two oxygen atoms (O2). Here there is four atoms of oxygen gas which in total gives eight oxygen atoms. Same ways One molecule of hydrogen gas is composed of two hydrogen atoms (H2), so 2 atoms of hydrogen gas in total gives four hydrogen atoms. As per the formula of water, 2 (H2) and 1(O) to form a water molecule (H2O). Here there are 4 H2, so divide the number of hydrogen atoms by the number needed per water molecule i.e. 4 / 2 = 2. This means 2 water molecules will be produced.