Question

What is the principal quantum number of the shell in which $f$-subshell first appears?

• A. $4$
• B. $3$
• C. $5$
• D. $6$

Answer 1

Answer: (A)

$4$

$1s$ $2s$ $2p$ $3s$ $3p$ $4s$ $3d$ $4p$ $5s$ $4d$ $5p$ $6s$ $4f$ $5d$ $6p$

$4f\Rightarrow$principal quantum no $n=4$