Litmus turns ___ in acid.

**The reasoning** Litmus is a natural indicator extracted from lichens. It's designed to show us whether a solution is acidic or basic by changing color. The rule is simple and must be memorized: - **Blue litmus → turns RED in acid** - **Red litmus → turns BLUE in base (alkali)** So when you dip blue litmus paper into an acidic solution (like lemon juice, vinegar, or dilute HCl), it turns **red**. This is your test for acidity. **Why the wrong options tempt you** **A) Blue** — This is what litmus turns in a *base*, not an acid. Students often mix up the two because both involve litmus, but the colors are opposite. **C) Green & D) Black** — These aren't litmus colors at all. You might be thinking of other indicators like universal indicator (which shows green at neutral pH), but litmus only switches between red and blue. **Quick takeaway** **"Acid = Red litmus"** — think of the 'A' in **A**cid and the 'R' in **R**ed. Lock this into your memory and you'll never confuse it again!