(A) : The most common oxidation state of lanthanides is + 3.
(R) : All Lanthanides have three electrons in their outermost f sub shell.

Given data:It is given to identify whether both given statements are correct or not.

Explanation:

Lanthanides are most frequently found in the stable oxidation state +3.
To achieve it, the outermost two 6s electron electrons and one 4f electron electron are removed. It is challenging to remove additional electrons from the 4f sub-shell due to the large energy gap between 4f and 6s. 

Hence, correct answer is: (C) A is true, R is false