An unknown solution turns blue litmus red and gives a gas with metal carbonate that turns lime water milky. What is the nature of the solution?

Correct answer: Acidic

Two independent observations identify the solution as acidic. First, an acid changes blue litmus to red. Second, an acid reacts with a metal carbonate to produce carbon dioxide: acid + carbonate → salt + water + CO2. The gas turns limewater milky because insoluble calcium carbonate forms. A basic or neutral solution would not normally give both of these characteristic tests, and “without nature” is not a scientifically meaningful classification.