To calculate the formula mass of S2Cl2, we need to add up the atomic masses of each atom in the molecule.

- The atomic mass of sulfur (S) is 32.066 g/mol.

- The atomic mass of chlorine (Cl) is 35.453 g/mol.

Since there are two sulfur atoms and two chlorine atoms in S2Cl2, we need to multiply the atomic mass of each element by the number of atoms of that element in the molecule.

Formula Mass of S2Cl2 = (2 * 32.066 g/mol) + (2 * 35.453 g/mol)

= 64.132 g/mol + 70.906 g/mol

= 135.038 g/mol

Therefore, the formula mass of S2Cl2 is 135.038 g/mol.