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:

Atomic number:

• The atomic number is defined as the total number of protons present in the nucleus or electrons in a neutral atom.
• It is denoted by $‘\mathrm{Z}’$.
• All atoms of an element have the same atomic number.

$\mathrm{Atomic}\mathrm{number}=\mathrm{number}\mathrm{of}\mathrm{protons}=\mathrm{number}\mathrm{of}\mathrm{electrons}$

Atomic number:

• The mass number is the sum of the number of protons and the number of neutrons present inside the nucleus.

$\mathrm{Mass}\mathrm{number}=\mathrm{number}\mathrm{of}\mathrm{protons}+\mathrm{number}\mathrm{of}\mathrm{neutrons}$

Hence, the correct option is (D).