Which unit of pressure is derived from the early barometers used to measure pressure?
mmhg
bar
pa
atm

mm Hg

Explanation:

In those early barometers the concept to measure the pressure was to find the displacement of the mercury in the barometer tube

So here in that barometer when mercury filled tube is inverted into the mercury filled container then the level of mercury is at some height

When we measure that height then it will help to find the pressure

since we used mercury in this experiment

so the length of the mercury in this tube is given as pressure units

so one of the unit is known as

mm Hg

i think the answer is a, hope this is right, that would be my best guess.

distance = 150m

displ = root (50 ^2 + 100^2)

root(2500+10000)

root 125000