Question

Which of the following statement is always correct?

• A. An atom has an equal number of electrons and protons.
• B. An atom has an equal number of electrons and neutrons.
• C. An atom has an equal number of protons and neutrons.
• D. An atom has an equal number of electrons, protons, and neutrons.

Answer 1

The correct option is A

An atom has an equal number of electrons and protons.

Explanation of the correct option:

(A) An atom has an equal number of electrons and protons

• An atom is electrically neutral.
• So the number of protons should be equal to the number of electrons.
• The number of protons in an electron, which is also equal to the number of electrons in an atom, is known as the atomic number (Z).
• Atomic number = number of proton(p) = Number of electron(e).

Explanation of incorrect options:

(B)An atom has an equal number of electrons and neutrons.

• In some cases, an atom has an equal number of electrons and neutrons.
• The mass number of an atom(M) is equal to the sum of the number of protons and neutrons in the nucleus.
• The number of neutrons is equal to the difference between the mass number of the atom(M) and the atomic number(Z).

(C)An atom has an equal number of protons and neutrons.

• If an atom has an equal number of protons and neutrons, then the mass number(M) will be twice the atomic number(Z).

(D)An atom has an equal number of electrons, protons, and neutrons.

• An atom has an equal number of protons and electrons.
• Isotopes are atoms with various numbers of neutrons in their atomic nuclei that belong to the same element (same number of protons).

Hence, option (A) is correct., an atom has an equal number of electrons, and protons are the correct option.