The composition of an atom P is 13. 11. 11 . What is the mass number?
To do this question we need to know these two things...
1) In an atom, number of electrons and protons are equal
Mass no = No. of protons + No. of neutrons.
Here two equal value given are 11, 11
So number of electrons and protons are 11
And the remaining 13 is the number of neutrons
Mass no =13 + 11