HELPP PLEASE
I just need help solving C

In the periodic system  

The group number in the periodic system is determined by the same valence electrons (main group), while the period is determined by the number of shells  

valence electrons :

Valence electrons for the main group:  Group 1,2,13-18

Lanthanides and actinides: Group 3–16  

Transition metals: Group 3–12  

1. Valence electron : 4s²

Group 2

Period 4

2. Valence electron : 2s²2p²

Group 14

Period 2

3. Valence electron : 3s²3p⁴

Group 16

Period 3

4. Valence electron : 4s²3d⁸

Group 10

Period 4

5. Valence electron : 5s²5p⁶

Group 18

Period 5

6. Valence electron : 7s²

Group Lanthanides and actinides (6)

Period 7

the mantle

explanation:

earth is divided into three layers: the crust or the outermost layer on which we live; the underlying, middle layer - the mantle - and the core (the innermost layer of earth).