Structure of the Atom — Science STD 9 — Question

Protons = 4Neutrons = 5
Number of protons = Number of electrons
Number of electrons = 4
Electronic Configuration
= 2, 2
Number of Valence electrons in the outermost shell = 2
Valency = 2

1. Since, protons =electrons = atomic no. 

So atomic no. is 4

2. Mass Number = No. of Protons + No. of Neutrons

= 4 + 5 = 9

3. Now electronic distribution, K = 2, L = 2

So as the outermost shell has 2 electrons, so the valency will be 2