Question

Which of the following statements are correct about Mendeleev ’s periodic table?
(i) It is based on increasing order of atomic numbers.
(ii) Mendeleev corrected the atomic weight of some elements like $ Be $ , $ In $ etc.
(iii) $ (Ar,{H_2}) $ , $ (Co,C{l_2}) $ , $ (Te,{F_2}) $ are three inverted pairs.
(iv) It is based on increasing order of atomic weights.
(A) Only (i) correct
(B) (ii) and (iv) are correct
(C) Only (iii) correct
(D) (i) and (iv) are correct

Answer 1

Hint : Mendeleev created his periodic table on the basis of periodic law which states that the physical and chemical properties of any element is a periodic function of their atomic weights. The use of atomic weights also helped Mendeleev in correcting the atomic weights of a few elements.

Complete Step By Step Answer:
Mendeleev ’s periodic table is based on periodic law which states that ‘the physical and chemical properties of elements are periodic functions of their atomic weights.’ Thus, Mendeleev’s periodic table uses the increasing order of atomic weights to place elements.
Hence, statement (i) is incorrect and (iv) is correct.
Mendeleev corrected the atomic weight of some elements like $ Be $ , $ In $ , $ Au $ , $ Pt $ etc based on their position in the periodic table. For example, the atomic mass of beryllium was corrected from $ 13.5 $ to $ 9 $ . Thus, statement (ii) is correct.
The inverted pairs in Mendeleev’s periodic table are $ (Ar,K) $ , $ (Co,Ni) $ and $ (Te,{I_2}) $ . These pairs are also called anomalous pairs since their positions are not justified in the table.
Thus, statement (iii) is incorrect.
Therefore, option B is the correct answer.

Note :
The important point in Mendeleev’s periodic table is based on the atomic weights not on atomic number, which is used in the modern periodic table. The arrangement according to atomic weight corresponds to the valency of the element and to a certain extent, the difference in their chemical behaviour like $ Li,{\text{ }}Be,{\text{ }}B,{\text{ }}C,{\text{ }}N,{\text{ }}O,{\text{ }}F $ .