Among the following oxides of p-block elements, number of oxides having amphoteric nature is ________.
Cl₂ O₇, CO, PbO₂, N₂ O, NO, Al₂ O₃, SiO₂, N₂ O₅, SnO₂

Solution

Chemistry ma’am · 4 steps

Sort the nine oxides into acidic, neutral and amphoteric, then count only the amphoteric group.

1. What amphoteric means. An amphoteric oxide reacts with both acids and bases. In the p-block these are the oxides of the elements just past the metal–non-metal border: Al, Ga, Sn, Pb.
2. Rule out the rest. Non-metal oxides in a high oxidation state are acidic. Oxides like CO, NO and N₂O react with neither acids nor bases, so they are neutral.

   Nature	Oxides from the list	Count
   Acidic	Cl₂O₇, N₂O₅, SiO₂	3
   Neutral	CO, N₂O, NO	3
   Amphoteric	Al₂O₃, SnO₂, PbO₂	3

3. Check one. Al₂O₃ dissolves in HCl to give AlCl₃ and in NaOH to give Na[Al(OH)₄]. SnO₂ and PbO₂ behave the same way, forming stannates and plumbates with alkali.
4. So. Only Al₂O₃, SnO₂ and PbO₂ are amphoteric, so the answer is 3.

The common slip: 4. Counting SiO₂ as amphoteric because it reacts with HF gives 4. That reaction is a special case: SiO₂ is an acidic oxide.

The idea to keep. Memorise the three neutral oxides (CO, NO, N₂O), call the remaining non-metal oxides acidic, and treat the oxides of Al, Ga, Sn and Pb as amphoteric.

Answer from the NTA final answer key. Solution by PrepWiser.