What is the atomic number of helium

2

Explanation:

Its atomic number is 2, so it has two protons in its nucleus.

atomic mass = 39

number of neutrons = 20

number of protons= 19

electronic configuration = 1s2 2s2 2p6 3s2 3p6 4s1

the number of electron in first shell = 2

number of electrons in n=3 shell = 8

answerspecific gravity;