You are on an island and need freshwater to drink. which process could you use to separate that salt from ocean water and provide freshwater for drinking?

Collect the salt water and put it in something where it can boil under fire or any other heat source capable to bring the water to boiling temperature. You can consume the collected water safely , but wait for its temperature to fall, except if you need it to be hot.

If you boil the water and transfer the vapor to a different container, then the salt will be left behind in the first tub, whereas the freshwater will be in the other container.  If you want specifics, then you can do the following:

Boil the salt water in a pot with a lid. Offset the lid slightly so that the water that condenses on the inside of the lid will run down the side to be collected in a separate container.

Once again, the salt cannot evaporate, so it is left behind in the pot as a solid.

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.