Question

Which of the following is not amphoteric in nature?

• A. \(NH_3\)
• B. \(HCl\)
• C. \(H_2O\)
• D. \(Cr_2O_3\)

Hint:

Common amphoteric substances include:
• \(H_2O\)
• \(Al_2O_3\)
• \(ZnO\)
• \(Cr_2O_3\) Strong acids like \(HCl\) and \(HNO_3\) are not amphoteric because they can only donate protons.

Answer 1

The Correct Option is B

Concept: An amphoteric substance is one that can behave both as an acid and as a base depending upon the reacting species. According to the Brønsted-Lowry concept:
• Acids donate protons \((H^+)\)
• Bases accept protons \((H^+)\) A substance capable of both donating and accepting protons is called amphoteric or amphiprotic. Some metal oxides also show amphoteric behavior because they react with both acids and bases.

Step 1: Checking the nature of \(NH_3\).
Ammonia \((NH_3)\) mainly acts as a base because it accepts a proton: \[ NH_3 + H^+ \rightarrow NH_4^+ \] Under certain conditions, it can also donate a proton very weakly. Hence, it can exhibit amphoteric behavior in advanced acid-base chemistry.

Step 2: Checking the nature of \(HCl\).
Hydrochloric acid is a strong acid: \[ HCl \rightarrow H^+ + Cl^- \] It donates protons very easily but does not accept protons. Therefore, it behaves only as an acid and is not amphoteric.

Step 3: Checking the nature of \(H_2O\).
Water is a classic amphoteric substance.
• It can donate a proton: \[ H_2O \rightarrow H^+ + OH^- \]
• It can also accept a proton: \[ H_2O + H^+ \rightarrow H_3O^+ \] Therefore, water is amphoteric.

Step 4: Checking the nature of \(Cr_2O_3\).
Chromium oxide reacts with both acids and bases.
• With acids, it behaves as a base.
• With bases, it behaves as an acid. Hence, \(Cr_2O_3\) is amphoteric.

Step 5: Final conclusion.
Among the given compounds, \(HCl\) behaves only as an acid and does not show amphoteric nature. Therefore, the correct answer is: \[ \boxed{(2)\ HCl} \]