What is the name of the measurement system used in America?.

On a day when the barometer reads 75.23 cm, a reaction vessel holds 250 ml of ideal gas at 20 celsius. an oil manometer ( ρ= 810 kg/m^3) reads the pressure in the vessel to be 41 cm of oil and below atmospheric pressure. what volume will the gas occupy under s.t.p.?

Give one example to show that when substances are mixed,it may result in a chemical or a physical change depending on the conditions.

Difference between series and parallel circuits