As the elements in period 3 are considered in order from sodium to chlorine, there is an increase in the 1) atomic radius
2) electronegativity
3) number of electrons in the first shell
4) number of electron shells

2 Electronegativity

Explanation:

Period 3 on the element table contains the following eight elements

ElementSymbolAtomic numberAtomic radius /nm

sodium         Na                11               0.191

magnesiumMg                12              0.160

aluminiumAl                13              0.130

silicon         Si                14               0.118

phosphorusP                15               0.110

sulfur         S                16              0.102

chlorine         Cl                17             0.099

argon         Ar                18             0.095

Sodium and magnesium, are members of the s-block of the periodic table

The rest are members of the p-block.

In the whole of period 3, the outer electrons are all in 3-level orbitals

Na[Ne] 3s1

Mg[Ne] 3s2

Al[Ne] 3s2 3px1

Si[Ne] 3s2 3px1 3py1

P[Ne] 3s2 3px1 3py1 3pz1

S[Ne] 3s2 3px2 3py1 3pz1

Cl[Ne] 3s2 3px2 3py2 3pz1

Ar[Ne] 3s2 3px2 3py2 3pz2

1) No

2) Yes

3) No

4) No

answer; 4 electrons;