Question

How many electrons, protons and neutrons are present in x+ , if atomic number of x is 19 and its mass number is 39?

Answer 1

electrons= 19
protons= 19
neutrons= 39-19=20

Answer 2

The Atomic number (Z) of any atom is the total no. of protons in the Nucleus. They are positively charged sub-atomic particles.

The Mass number (A) is the total no. of protons and neutrons (i.e. nucleons) in the nucleus.

Remember! In a neutral atom, the number of protons is equal to the number of electrons to balance the electrical charge on the atom.

Then:-

No. of sub-atomic particles:

No. of protons = 19

No. of electrons = 19 (Same as no. of protons)

No. of neutrons = 39 - 19 = 20

Note:-

The no. of protons is equal to the no. of electrons in an neutral atom but in case of ions and radicals, due to the gain and loss of electrons, the relative number of electrons and protons is unequal.