Question

Which one of the following does not contain electrons in $5f$ subshells?

• A. $Th(Z=90)$
• B. $Lr(Z=103)$
• C. $U(Z=92)$
• D. $Cm(Z=96)$

Answer 1

Answer: (A)

$Th(Z=90)$

$Th$ configuration is $[Rn{]}^{86}6d^{2}7s^2$

According to Afbau principle $5f$ subshell cannot filled before $6d$ and $7s$

So that $Th$ not contain $5f$ subshell