Answer:
Neutrons = ( Atomic mass – Atomic number ) ( A–Z )
Protons and Electrons are equal to the atomic number
For example Neon,
Mass number (A) = 20
Atomic Number (Z) = 10
Number of Protons = 10
Number of Electrons = 10
Number of Neutrons = ( A–Z ) = 10
Electronic distribution :
K= 2
L= 8
