Question

Which belongs to the actinides series?

• A. $Ce$
• B. $Cf$
• C. $Ca$
• D. $Cs$

Answer 1

Answer: (B)

The fourteen elements which follow actinium from thorium $(Z=90)$ to lawrencium $(Z=103)$ are called actinoids.
They involve the filling of $5f-$ subshell.
Californium $(Cf)$ has the atomic number $98$ and its configuration is as
$Cf(Z=98):[Rn]5f^{10},6d^0,7s^2$
Hence, it is a member of actinides series.