For a mercury barometer, the change in level of mercury in the tube is due to the change in ____.
atmospheric pressure
A barometer is a device which is used to measure the atmospheric pressure. It consists of a glass tube closed at one end immersed in a container filled with mercury. A scientist named Torricelli discovered that the change in the level of mercury in the tube is due to the change in atmospheric pressure. When the air pressure outside the barometer is high, it pushes down the mercury in the container, which pushes the mercury in the test tube and raises its level. So, option (D) is the correct answer.