The answer is "1.99 x 10²⁴ sulfur atoms".
In one mole of compound there are Avogadro's number of atoms that is 6.02 x 10²³
So in 1.10 mol of aluminum sulfide there are = 1.10 x 6.02 x 10²³ = 6.622 x 10²³
The formula of Aluminum Sulfide Al₂S₃, it means there are three sulfur atoms per formula unit.
So, sulfur atoms in Al₂S₃ = 6.622 x 10²³ x 3 = 19.9 x 10²³ = 1.99 x 10²⁴
