Final answer:
In a barometer, a column of mercury at 77.5 cm corresponds to a much greater height when water is used, due to water's lower density. A mercury barometer needs to be only 1/13.6 as tall as a water barometer to measure the same atmospheric pressure, leading to the conclusion that the height would be more than 77.5 cm for water.
Step-by-step explanation:
If the height of mercury in a barometer is 77.5 cm, the height of water that would reach in a water barometer would be more than 77.5 cm. Mercury has a density approximately 13.6 times greater than that of water. Therefore, under the same atmospheric pressure, a mercury barometer only needs to be 1/13.6 as tall as a water barometer. Given the standard atmospheric pressure at sea level is 101,325 Pa, which corresponds to a mercury column of approximately 760 mm high, a water barometer would need to support a column of water over 10 meters high, which would be very impractical for a barometer design. The correct answer is: c) More than 77.5 cm.