Answer:
no. of protons = 39
atomic number = number of protons = 39
number of neutrons = 51
element is Yttrium
Explanation:
given data:
number of electron is 39
mass of atom is 90
We know that atoms are neutral because +ve charged protons is equal to no of -ve charged electrons.
we know that:
atomic number is equal to number of protons,
and atomic mass is the summation of no. of protons and no. of neutrons
number of protons = number of electrons
from the data given:
a) No. of protons = 39 (since number of electrons = protons)
b) atomic number = number of protons = 39
c) number of neutrons = atomic mass - atomic number
= 90 - 39
= 51
d) element is Yttrium
