Is this true or false about the characteristics of a substance? a certain substance will always be made up of the same element or compound.

A chemical substance is defined as the substance which is made up of single molecule or atom.

Thus, the given statement is true.

Now, law of multiple proportions: The combination of two elements with each other to give two or more compounds, the mass ratio of one element which combines with the fixed mass of another element are present in form of simpler whole numbers. For example: and .

Hence, a substance is made up of the single element or compound.

it should be p1 v1 = p2 v2

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.