Identifying ammonium carbonate via diagnostic reactions

Steps:

• Fizzing with HCl shows CO2 gas from carbonate or bicarbonate ions.
• Gas turning litmus blue with hot NaOH identifies ammonia from ammonium ions.
• R requires both ammonium (for NH3) and carbonate/bicarbonate (for CO2) components.
• Among options, (NH4)2CO3 satisfies both without side reactions producing other gases.

Why B is correct:

• (NH4)2CO3 reacts with HCl to evolve CO2 (fizzing) and with hot NaOH to evolve NH3 (turns litmus blue), per standard salt decomposition equations.

Why the others are wrong:

• A. NH4Cl has no carbonate/bicarbonate, so no CO2 fizzing with HCl.
• C. NH4HCO3 decomposes on heating to release CO2 (turns litmus red) with NH3, complicating the litmus test.
• D. (NH4)2SO4 has no carbonate/bicarbonate, so no CO2 fizzing with HCl.

Final answer: B