Question

Atomic number of a few elements are given below:

10, 20, 7, 14

Identify the period to which these elements belong?

• A. 2, 4, 2, 3.
• B. 3, 2, 3, 2.
• C. 2, 2, 3, 3.
• D. 3, 3, 2, 2.

Answer 1

The correct option is A 2, 4, 2, 3.

The period is determined by writing the electronic configuration of the element. The highest value of principal quantum number determines the period to which the element belongs.

If the atomic number of the element is 10, the electronic configuration is 1s² 2s² 2p^{6 .}

^{Since the highest principal quantum number (n) is 2, the element belongs to the second period.}

If the atomic number of the element is 20, the electronic configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s²

Since the highest principal quantum number (n) is 4, the element belongs to the fourth period.

If the atomic number of the element is 7, the electronic configuration is 1s² 2s² 2p³ .

Since the highest principal quantum number (n) is 2, the element belongs to the second period.

If the atomic number of the element is 14, the electronic configuration is 1s² 2s² 2p⁶ 3s² 3p².

Since the highest principal quantum number (n) is 3, the element belongs to the third period.