Question

Sulphur atom in sulphur trioxide has sextet of electrons

Answer 1

16 is the answer. hope it helps u

Answer 2

Sulphur element has D-shell available for bonding.That is why it can form six bonds and have an expanded octet.Oxygen on other hand uses p shell for bonding which is completely filled by sharing 2 electrons.As to why sulfur expands, Sulphur has vacant d orbitals lying with comparable energy to the bonded ones