Question

why should the lower meniscus be read while measuring the volume of colourless or transparent liquids but the upper meniscus while using colured ones??

Answer 1

The lower meniscus must be read while measuring the volume of colourless or transparent liquids but the upper meniscus while using colured ones because the phase boundary in the colourless liquid is clearly visible so it is easy to read it. Where as in coloured liquid the lower meniscus is not visible clearly so upper meniscus should be observed.