An atom has atomic number 11 and mass number 23. How many electrons does the atom have?

23

22

12

11

No. of electrons in an atom is equal to atomic number of the element. So no. of electrons in sodium is 11. Secondly, no. of neutrons = mass number - no. of protons. As protons are equal to electrons so 23 - 11 = 12.

Answer: 11

Explanation:

Mass number is defined as the sum of number of protons and neutrons that are present in an atom.

Mass number = Number of protons + Number of neutrons

Atomic number is defined as the number of protons or number of electrons that are present in an atom.

Atomic number = Number of electrons = Number of protons

Hence, number of electrons is equal to the atomic number which is 11.