A flask containing helium gas is connected to an open-ended mercury manometer. The open end is exposed to the atmosphere, where the prevailing pressure is 752 torr. The mercury level in the open arm is 47 mm above that in the arm connected to the flask of helium. What is the helium pressure, in torr?

The helium pressure is 799 torr.

Explanation:

It is known that 1 mm Hg is equal to 1 torr. As we are given an open-ended mercury manometer so, its pressure will also be equal to the atmospheric pressure which is given as 752 torr.

And, it is given that pressure of mercury level in the open arm is 47 mm above that in the arm connected to the flask of helium. Therefore, adding both the pressures we will get the pressure of helium as follows.

                (752 + 47) mm Hg

              = 799 mm Hg

or,           = 799 torr

Thus, we can conclude that the helium pressure is 799 torr.

i think it's c. if you look search electronic symbol on google and then click on wiki it shows you a