Question

write first 20 elements ,their valency ,atomic noand mass number

Answer 1

Element-Atomic no.-mass no.; Valancy
H-1-1-1
He-2-4-0
Li-3-7-1
Be-4-9-2
B-5-11-13
C-6-12-4
N-7-14-3
O-8-16-2
F-9-19-1
Ne-10-20-0
Na-11-23-1
Mg-12-24-2
Al-13-27-3
Si-14-28-4
Ph-15-31-3
S-16-32-2
Cl-17-35.5-1
Ar-18-40-0
K-19-39-1
Ca-20-40-2