Question

A neutral atom has 9 electrons and mass number is 19.

Q: Answer-A neutral atom has 9 electrons and mass number is 19. What is the number of neutrons in the atom?

Mass number of an atom is defined as the sum of protons and neutrons present in the nucleus. Since, the number of electrons are 9 and the atom is neutrons, therefore number of protons will also be equal to 9. Mass number is equal to protons neutrons19. Putting protons as 9, we get number of neutrons as 10. Hence, option B is correct.