Question

Which of the following are true for an element?

(i) Atomic number$=$number of protons$+$number of electrons

(ii) Mass number$=$number of protons$+$number of neutrons

(iii) Atomic mass$=$number of protons$+$number of neutrons

(iv) Atomic number$=$number of protons$=$number of electrons

• A. (i) and (ii)
• B. (i) and (iii)
• C. (ii) and (iii)
• D. (ii) and (iv)

Answer 1

The correct option is D

(ii) and (iv)

Explanation for correct option:

Option (D): (ii) and (iv):

Mass number:

Mass number of an element is equal to the sum of number of protons and number of neutrons in a atom.

Thus,

Mass number$=$number of protons$+$number of neutrons

Atomic number:

Atomic number of an element is equal to the number of protons and number of electrons in an atom.

Thus,

Atomic number$=$number of protons$=$number of electrons

Thus, (ii) and (iv) are correct

Explanation for incorrect option:

Option (A): (i) and (ii):

Atomic number is not equal to the sum of number of protons and number of electrons.

Thus, (i) is not correct.

Option (B): (i) and (iii):

Atomic number is not equal to the sum of number of protons and number of electrons.

Thus, (i) is not correct.

Atomic number is not equal to the sum of number of protons and number of neutrons.

Thus, (iii) is not correct.

Option (C): (ii) and (iii):

Atomic number is not equal to the sum of number of protons and number of neutrons.

Thus, (iii) is not correct.

Thus, Option (A) is the correct option.