Question

The principal quantum number describe?

• A. Shape of orbital
• B. Size of the orbital
• C. Spin of an electron
• D. Orientation in the orbital electron cloud

Answer 1

The correct option is B

Size of the orbital

Explanation of correct option.

Option (B ) Size of the orbital

• The principal quantum number is one of four quantum numbers assigned to each electron in an atom to describe that electron's state.
• Its values are natural numbers (from 1) making it a discrete variable.
• It is used to describe the size of the orbital.

Explanation of incorrect options:

Option (A) Shape of the Orbital

• The angular quantum number ($\mathrm{l}$) describes the shape of the orbital.
• Orbitals have shapes that are best described as spherical ($\mathrm{l}=0$), polar ($\mathrm{l}=1$), or cloverleaf ($\mathrm{l}=2$).
• Hence, incorrect option.

Option (C) Spin of the orbital

• An electron in an atom is completely described by four quantum numbers: $\mathrm{n},\mathrm{l},{\mathrm{m}}_{\mathrm{l}}$, and ${\mathrm{m}}_{\mathrm{s}}$. The first three quantum numbers define the orbital and the fourth quantum number describes the intrinsic electron property called spin.
• Hence, incorrect option.

Option (D) Orientation in the orbital electron cloud.

• Magnetic Quantum Number ($\mathrm{m}$) gives the orientation of the orbital in space.
• Hence, incorrect option.

Therefore, option (B) is the correct answer.