What is the valency of magnesium with atomic number 12 and sulphur with atomic number 16?

Explain why the valency of magnesium with atomic number 12 is 2 and that of sulphur with atomic number 16 is also 2?

What is the atomicity of sulphur?

What is atomic number and mass number?

What is the limitation of Rutherford atomic model?

What is the atomic number of carbon?

What is the mass of 1 mole of nitrogen atoms?

What is the change of atomic number Z of a nucleus when it emits a beta particle?