Question

let me answer of question 5

Answer 1

given.. no. of electrons = 10
no. of neutrons = 10
as no. of electrons = no. of protons
thus no. of protons = 10
therefore mass no. no. of neutrons + no. of protons .
mass no. 10 +10 = 20amu or 20mg

Answer 2

Mass number=e+n=10+10=20