Question

Elements A, B and C belong to the same period in the long form of the periodic table. The nature of the oxides of A, B and C is amphoteric, basic and acidic respectively. The correct order of the atomic numbers of these elements is :

• A. $C>B>A$
• B. $C>A>B$
• C. $A>B>C$
• D. $B>A>C$

Answer 1

The correct option is B $C>A>B$

Acidic oxides are formed by those metal cations which have higher polarizing power due to higher effective nuclear charge, and metal cations with the lesser polarizing power are amphoteric and basic oxides are formed by the cation which have least polarizing power.

Now, as the polarizing power is directly proportional to the effective nuclear charge, and given that A, B and C are belonging to the same period, so now as we know, left to right the effective nuclear charge increases due to decrease in size, so polarizing power increases left to right ( with increase in atomic number) so if C is acidic, it has highest atomic number.

A is amphoteric, so it has a lesser atomic number than the C and B is basic, so it has the least atomic number.

Hence, the order is as follows :

C > A > B

Hence the correct option is B.