Two atoms total are in NaCl.
Answer: The empirical formula is 
Explanation:
If percentage are given then we are taking total mass is 100 grams.
So, the mass of each element is equal to the percentage given.
Mas of H = 1.8 g
Mass of S = 56.1 g
Mass of O = 42.1 g
Step 1 : convert given masses into moles.
Moles of H =
Mass of S =
Moles of O=
Step 2 : For the mole ratio, divide each value of moles by the smallest number of moles calculated.
For H =
For S =
For O =
Converting to whole number ratios
The ratio of H: S: O= 2: 2: 3
Hence the empirical formula is 
Answer:
water because the other two were formed through a chemical process