How to make water level indicator

(a). What is a universal indicator? For what purrpose is it used? (b). How does a universal indicator work? (c). Water is a neutral substance. What colour will you get when you add a few drops of universal indicator to a test-tube containing water?

Water pollution indicator is:

A wooden block is floating on water at 1^@C with volume v above the water level. If the temperature of water starts increasing slowly, how will the volume of block above the water level is affected?

Contamination of water sewage is indicated by cysts of

A block of wood is floating in water at 0^@ C . The temperature of water is slowly raised from 0^@ C to 10^@ C . How will the precentage of volume of block above water level change with rise in temperature?