The correct answer is turn blue litmus red.Concept:Acids have a sour taste and change the colour of blue litmus to red, whereas bases are bitter in taste and change the colour of the red litmus to blue. Litmus is a naturally occurring indicator.When a solution causes no change in the colour of the litmus solution, it is said to be a neutral solution. It has neither an acidic nor a basic nature.Explanation:Ammonium chloride is a by-product of sodium carbonate.It is a white crystalline salt with the chemical formula NH4Cl that is highly soluble in water.Ammonium chloride is formed by the neutralization reaction strong acid, hydrochloric acid, and a weak base, ammonium hydroxide. This indicates that the ammonium chloride is acidic. Ammonium chloride thus turns blue litmus red.