Litmus tests reveal acid-base nature of reaction products and gases

Steps:

• Ammonium carbonate reacts with dilute HCl to form ammonium chloride, CO2, and water, yielding an acidic solution from excess strong acid.
• In experiment 1, acidic solution contacts litmus: blue turns red, red stays red, so both red.
• In experiment 2, evolved ammonia gas (NH3) is basic due to its ability to accept protons.
• Basic ammonia contacts litmus: red turns blue, blue stays blue, so both blue.

Why C is correct:

• Litmus color change follows acid-base indicator rules: acids protonate to red, bases deprotonate to blue; HCl mixture is acidic (red), NH3 gas is basic (blue).

Why the others are wrong:

• A: Experiment 1 mixture is acidic, not basic, so not both blue.
• B: Experiment 2 ammonia is basic, not acidic, so not both red.
• D: Experiment 2 ammonia is basic, not acidic, so not both red.

Final answer: C