Question

Identify the element so that the last electron enters in ( \(n-2\) )f sub shell.

• A. Au
• B. Hg
• C. W
• D. No

Hint:

Elements in which the last electron enters the (n-2)f subshell are the f-block elements.

Answer 1

The Correct Option is D

Step 1: Block Check
Au ($5d^{10}6s^{1}$), Hg ($5d^{10}6s^{2}$) and W ($5d^{4}6s^{2}$) fill $5d$.

Step 2: Nobelium
No has configuration $[\text{Rn}]5f^{14}7s^{2}$, where the last electron enters $5f$, which is the $(n-2)f$ subshell for $n=7$.

Step 3: Result
Option (D).

Final Answer:
The element is No. \[ \boxed{\text{(D) }\text{No}} \]