Question

Which of the following statements are correct?
(i) The second period $(n=2)$ starts with lithium and third electron enters the $2s$ orbital.
(ii) Successive filling of $3s$ and $3p$ orbitals gives rise to the third period of 8 elements from sodium to argon.
(iii) The fourth period $(n=4)$ starts at potassium and the added electron fill up first $4s$ and $4p$ orbitals then $3d$ orbital is filled.
(iv) Fifth period begins with rubidium with the filling of $5s$ orbital and ends at xenon with the filling up of the $5p$ orbital.

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

Answer 1

Answer: (D)

In fourth period filling up of $3d$ orbital becomes energetically favourable before the $4p$ orbital is filled.