Question

An atom of sodium has an atomic number of 11 and a mass number of 23. Which of the following statements is correct?

• A. An atom of sodium has 11 protons, 11 electrons, and 11 neutrons.
• B. An atom of sodium has 10 protons, 10 electrons, and 12 neutrons.
• C. An atom of sodium has 11 protons, 11 electrons, and 12 neutrons.
• D. An atom of sodium has 10 protons, 10 electrons, and 13 neutrons.

Answer 1

The correct option is C

An atom of sodium has 11 protons, 11 electrons, and 12 neutrons.

The number of protons is equal to the number of electrons to maintain the electrical neutrality of atom. So number of proton = number of electron = atomic number = 11

Mass number = Number of protons (Atomic number) + Number of neutrons

Let $x$ be the number of neutrons

$23=11+x\Rightarrow x=12$