What is the mettalliod in peiod three with more protons tha sodium and fewer valence electrons than chlorine?

             Silicon

Explanation:

Atomic Mass (# of protons) of Si  =  14

Valence Electrons in Si;
     
                                    1s², 2s², 2p⁶, 3s², 3p²

Hence in third shell (valence shell) there are four valence electrons.

As we know Sodium has atomic number 11 so it has 11 protons, therefore, Si has greater number of protons (14) than Na.

Also, number of valence electrons in Chlorine are 7, so Silicon has less number of valence electrons (4) as compared to Cl.

Which metal is less dense

The answer to that would be magnesium