Question

an atom has 31 electrons, 39 neutrons and 31 protons. it follows that it mass number is
a)31
b)70
c)62
d)39

Answer 1

Answer:

70

Explanation:

Mass number = no. of protons + no. of neutron

=> 31 + 39  = 70

Therefore the Mass Number = 70

Answer 2

The mass number of the atom is 70.

• The atomic number of an atom is defined as the number of protons present in it.
• The mass number of an atom is the sum of the number of protons and the number of neutrons.
• The atom has 31 protons and 39 neutrons hence its mass number is 31+39=70.
• Hence the correct option is b.