The graph below shows how the pressure and volume of a gas vary when the
number of moles and the temperature of the gas are held constant. what
happens to the pressure inside a sealed syringe of gas as the volume of the
syringe increases?
(sorry the picture sucks)

The pressure of the gas decrease as the volume increases.

Option A.

The Boyle's law states that in a situation of constant volume and constant temperature, as the pressure of an ideal gas increase, the volume decreases and vice versa. So the mass and the temperature remaining constant, the pressure and the volume of an ideal gas are inversely proportional.

So P ∝ 1/V.

Thus, inside a sealed tube, the mass of the gas is constant. The temperature of the region is said to be constant under the short span of time of this experiment. So as the syringe is pulled, the volume do increase, so the pressure inside the vial decrease.

This is what is plotted in the graph which gives a rectangular hyperbola.

a mercury barometer is a device that uses the physical properties of mercury in a tube to measure barometric pressure. mercury barometers are used for : -

1. measurement of atmospheric pressure  

2. determining the altitude of a place

3. weather forecasting

4. calibration and checking of aneroid barometers

5. application in fluid mechanics

6. measurement of pressure in aircrafts

7. surface weather analysis

8. preparation of barographs

9. usage in physical sciences like physics, astronomy & chemistry

10. preparation of aircraft altimeters

characteristics of mercury barometer : -

1.used to define and measure atmospheric pressure.

2.on the average at sea level the column of mercury rises to a height of about 760 mm.

3.this quantity is equal to 1 atmosphere.

4.it is also known as standard atmospheric pressure.

5.a barometer in which the weight of a column of mercury in a glass tube with a sealed top is balanced against that of the atmosphere pressing on an exposed cistern of mercury at the base of the mercury column, the height of the column varying with atmospheric pressure.