Question

Which is not anomalous pair of elements in the Mendeleev's periodic table?

• A. $Ar$ and $K$
• B. $Co$ and $Ni$
• C. $Te$ and $I$
• D. $Al$ and $Si$

Answer 1

The correct option is D $Al$ and $Si$

Anomalous pairs are those pairs of elements in which the increasing order of atomic masses was not obeyed. Mendeleev placed these elements according to a similarity in properties and not in the increasing order of their atomic mass.
(A) $Ar$ ( at mass = 39.9) is placed before $K$ (at mass = 39.1)
(B) $Co$ (at mass = 58.9) is placed before $Ni$ (at mass = 58.6)
(C) $Te$ (at mass = 127.6 ) is placed before $I$ (at mass = 126.9).
(D) $Al$ and $Si$ is not anomalous pair of elements in the Mendeleev's periodic table. $Al$ (at mass = 26.98) is placed before $Si$ (at mass = 28.4) means $Al$ and $Si$ are in increasing order of their atomic masses. Therefore they are not Anomalous pair.