Which substance shows the correct indicator colour? Substance pH Indicator Colour (A) Stomach acid 2 Methyl orange Yellow (B) Lemon juice 3 Phenolphthalein Pink (C) Soda water 4 Phenolphthalein Pink (D) Seawater 8 Methyl orange Yellow - HSC - SSCE Chemistry - Question 3 - 2010 - Paper 1

To determine which substance shows the correct indicator colour, we need to examine the pH and the corresponding indicator:

1. Stomach acid (pH 2, Methyl orange): Methyl orange turns yellow in acidic conditions (pH < 3).

   • Correct colour: Yellow

2. Lemon juice (pH 3, Phenolphthalein): Phenolphthalein is colourless in acidic conditions (< 7), and turns pink in neutral to basic conditions (pH > 8).

   • Incorrect colour: Pink

3. Soda water (pH 4, Phenolphthalein): Same as lemon juice, Phenolphthalein would be colourless.

   • Incorrect colour: Pink

4. Seawater (pH 8, Methyl orange): Methyl orange turns yellow in acidic conditions. At pH 8, it would be colourless to orange (neutral or slightly basic).

   • Incorrect colour: Yellow

Based on this analysis, the correct match for an indicator colour is only found with Stomach acid.