How would you confirm that a colourless liquid given to you is pure water?

Answer :  For a given atmospheric pressure, every liquid has a distinct boiling point. Water in its pure form  boils at 100° C or 273 K at 1 atmospheric pressure. If given colourless liquid starts boiling below or above 100° C or 273 K, it is either not pure water or some other liquid. So boiling point of a liquid, is an indicator of its purity  at a particular atmospheric pressure.

This is an answered question from Chapter 2. IS Matter Around Us Pure ? of CBSE Class 9th Science

Check for Complete Exercise Solution for Chapter 2. IS Matter Around Us Pure ? | CBSE Class 9th Science