Which one of the following is ' d ' -block element?

Step-by-step solution

The element in which last electron enters in d -orbital is called d -block element. The electronic configuration of the given elements are as follows aligned Gd (64) & =[ Xe ] 6 s^2, 4 f^7, 5 d^7 Hs (108) & =[ Rn ] 7 s^2, 5 f¹⁴, 6 d^6 aligned aligned & Es (99)=[ Rn ] 7 s^2, 5 f¹¹ & Cs (55)=[ Xe ] 6 s^1 aligned Thus, Hs is a d-block element.