A drop of colourless liquid was placed on blue litmus paper. The litmus paper turned red. The liquid could be:

A colourless liquid truns neither blue litmus red nor red litmus blue

A student placed a few drops of a liquid over a portiin of the red litmus paper as shwon here. He observed that the red litmus paper turned blue. The liquid could b:

Blue litmus turns red in

Sulphuric acid turns blue litmus red.