One atom of K3919 contains:
(P-proton, n-neutron and ¯e-electron)
K3919 contains P = 19; ¯e=19;n=20
Representation of a Element E
EMassNo.AtomicNo.
Number of neutrons = Mass number-Atomic number
=39-19=20
Solve: n+5=19(n−1)