Question

Which of the following is not an anomalous pair?

• A. $S,Cl$
• B. $Te,I$
• C. $Co,Ni$
• D. $Ar,Ne$

Answer 1

Answer: (A), (D)

The correct options are
A $S,Cl$
D $Ar,Ne$

The following are not anomalous pairs.
(A) S (32.1), Cl (35.5)
(D) Ar (39.9), Ne(20.2)
The following are anomalous pairs.
(B)Te (128), I (127)
(C) Co(58.9), Ni (58.7)
The numbers in the bracket indicates atomic masses.
In the anomalous pairs of Mendeleev's periodic table, the elements having higher atomic masses are placed before the elements having lower atomic masses.
Ar(39.9), K(39) and Th (232), Pa(231) are also the anomalous pairs.