(B) The correct answer is $B$. $Pm$ (Promethium) is a lanthanoid,not an actinoid. $Pm$ is the only radioactive element among the lanthanoids. All acti

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$Pm$ is a radioactive element among actinoids.

(B) The correct answer is $B$. $Pm$ (Promethium) is a lanthanoid,not an actinoid. $Pm$ is the only radioactive element among the lanthanoids. All actinoids are radioactive. Therefore,the statement that $Pm$ is a radioactive element among actinoids is incorrect.

Class 12 Chemistry d-and f-Block Elements Lanthanoids and Actinoids

Easy

Which statement is incorrect with reference to inner transition elements?

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A
The oxides of lanthanoids are basic.
B
$Pm$ is a radioactive element among actinoids.
C
The values of ionisation enthalpy of actinoids are less than the values of ionisation enthalpy of lanthanoids.
D
Only in the electronic configuration of lanthanoids like $Ce, Gd, Lu$ the electrons are filled in $5d$ orbitals.