Helium atom has an atomic mass of 4u and two protons in its nucleus. How many neutrons does it have?

Helium atom has an atomic mass of 4 u and two protons in its nucleus. How many neutrons does it have?

Helium atom has an atomic mass of 4 u and two protons in its nucleus. How many neutrons does it have ?

Helium atom has an atomic mass of 4 u and two protons in its nucleus. How many neutrons does it have?

Helium atom has an atomic mass of 4 u and two protons in its nucleus. Howmany neutrons does it have ?

Lithium atom has atomic mass 6 and has 3 protons in it nucleus. How many neutrons does it have? Write down its electronic configuration.