VALENCE ELECTRONS :
The outer most energy level in an atom is called valency shell and electrons placed in this shell known as valence electrons.
Silicon (si) : 3s² 3p² ( Ne).
so, calculate the no.of electrons which are in power part. so 2+2 = 4.
silicon valence electrons= 4.
Oxygen : 1s² 2s² 2p⁴.
so, calculate the no. of electrons which are in the power part. so, 2+2+4 = 6.
so, oxygen valence electrons = 6.