Question

water cannot be used instead of mercury in a baraometer

Answer 1

Answer:

water cannot be used as barometric liquid because it's density is lower than Mercury

Answer 2

Answer:

Mercury is commonly used in barometers because its high density means the height of the column can be a reasonable size to measure atmospheric pressure. A barometer using water, for instance, would need to be 13.6 times taller than a mercury barometer to obtain the same pressure difference.