$A$ liquid boils when its vapour pressure equals

What is the pressure in $atm$ on a swimmer $10\; m$ below the surface of a lake?

$A$ $U$-shaped tube is partially filled with an incompressible liquid of density $1.2 \ g \ cm^{-3}$. Oil, which does not mix with the liquid, is poured into the left side of the $U$-tube until the liquid rises by $15 \ cm$ on the right side. If the density of the oil is $0.9 \ g \ cm^{-3}$, the oil level will stand higher than the liquid level on the right side of the $U$-tube by: (in $cm$)

During blood transfusion,the needle is inserted into a vein where the gauge pressure is $2000 \; Pa$. At what height (in $m$) must the blood container be placed so that blood may just enter the vein? (Density of whole blood,$\rho = 1.06 \times 10^{3} \; kg \; m^{-3}$,$g = 9.8 \; m \; s^{-2}$)

Who devised for the first time,a method for measuring atmospheric pressure?

The heights of mercury in a barometer at the base and at the top of a mountain are $75 \, cm$ and $50 \, cm$,respectively. If the ratio of the density of mercury to the density of air is $10^4$,what is the height of the mountain?