Rohit dips both red and blue litmus paper into a salt solution, and neither changes colour at all

Why

Rohit's expectation makes sense if he assumes litmus is supposed to change colour every single time it touches a liquid — a reasonable assumption if he's only ever seen litmus paper described as a colour-changing test. But litmus paper is answering a genuine three-way question, not just 'yes it reacted' or 'no it's broken': is this acidic, basic, or neither? Acids turn blue litmus red; bases turn red litmus blue; and NEUTRAL substances — like common salt water, or pure water — do neither, because they are neither acidic nor basic, sitting exactly in the middle. No colour change with BOTH papers is itself a clear, working result: it tells you the solution is neutral, which is real, useful information, not a failure of the test. Test: try the same pair of litmus papers on lemon juice (which turns blue litmus red) right after testing the salt water — if they still work correctly on the lemon juice, they were never faulty. His sister is right: no change on either paper is the correct outcome for a neutral substance, and that IS an answer, not broken equipment.