Question

Which of the given elements belong to the same period?

(i) A (Z = 2) (ii) B (Z = 3) (iii) C (Z = 6) (iv) D (Z = 10) (v) E (Z = 30).

Z is used to denote atomic number.

• A. A, B, C
• B. B, C, D
• C. B, D, E
• D. B, A, E

Answer 1

The correct option is B B, C, D

Elements present in the same period, have the same number of shells.
Electronic configuration of A- $1s^2$.
Electronic configuration of B- $1s^{2}2s^1$.
Electronic configuration of C- $1s^{2}2s^{2}2p^2$.
Electronic configuration of D- $1s^{2}2s^{2}2p^6$.
Electronic configuration of E- $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}$

For A, first shell is filled so it belongs to the first period.

For B, C, D, second shell is also filled, so they belong to the second period.

For E, electrons are filled till the fourth shell, so it belongs to the fourth period.

Hence, the elements B, C, D belong to same period.