Question

answer the question

Answer 1

mass number - atomic number= 20
the composition of the nucleus is 20

Answer 2

so here,
atimic number= no.of protons =19
mass number = no. of protons +no.of neutrons
39=19+no. of neutrons
no. of neutrons=39-19=20
Also in a neutral atom
no. of protons=no. if electron=19
hence compostion of nucleus is...
neutron=20
proton=19,

electron=19
electronic configuration is...
shell electron
k 2
l 8
m 8
n 1