What are indicators? Name the kinds of indicators, with one example of each and its colour or smell in acid and base.

1. 1 · Define in one line. An indicator is a substance that shows whether a solution is acidic or basic by a change in colour or smell.
2. 2 · Natural indicators. Litmus (from lichen): blue turns red in acid, red turns blue in base. Turmeric turns reddish-brown in a base.
3. 3 · Synthetic indicators. Phenolphthalein: colourless in acid, pink in base. Methyl orange: red in acid, yellow in base.
4. 4 · Olfactory indicators. Onion, vanilla essence and clove oil lose their smell in a base.
5. 5 · Link to real life. A turmeric curry stain turns reddish-brown when scrubbed with soap.
6. 6 · Close in one line. So indicators let us test acids and bases safely, without tasting them.

Scoring tip: A three-column table (indicator, in acid, in base) is quick to write and easy to mark.