Answer: 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, Â Â Â Â Â = 799 torr
Thus, we can conclude that the helium pressure is 799 torr.