Answer:
15.9994 amu
Explanation:
By definition 1 mole of any substance is the mass that contains 1 Avogadro's Number of particle. (=> 6.02 x 10²³ particles/mole).
1 mole Oxy => 15.9994 amu => contains 6.02 x 10²³ particles Oxy /mole
1 mole Sulfur => 32.064 amu => contains 6.02 x 10²³ particles Sulfur /mole
1 mole H₂O => 18 amu => contains 6.02 x 10²³ molecules of water / mole.