Question

Assertion : The 19^th electron in potassium atom enters into the 4s-orbital and not into the 3d-orbital.

Reason: (n + l) rule is followed for determining the orbitals of the lowest energy state

(a) Both A and R are true and R is the correct explanation of A  

(b) Both A and R are true but R is not correct explanation of A  

(c) A is true but R is false  

(d) A and R are false

Answer 1

Correct option (a) Both A and R are true and R is the correct explanation of A  

Explanation:

According to Aufbau's principle, the unfilled shell with lowest (n + l) value will be filled first. Therefore 4s orbital is filled first than 3d orbital. 

For 4s - orbital, (n + l) = 4 + 0 = 4 

For 3d - orbital, (n + l) = 3+2 = 5