Question

How many electrons in copper atom ${(}_{29}Cu)$ have $(n+l)=4$

• A. 6
• B. 7
• C. 8
• D. 4

Answer 1

Answer: (B)

${}_{29}CU$ is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{10}4s^1$.
The electrons having $(n+l)=4$ are present in $3p$ and $4s$ shells. Hence total number of such electrons is $7$.