Which of the following is true of a balanced chemical equation? A) The total number of molecules of reactants has to be the same as the total number of product molecules
B) the total number of atoms in the reactant molecules doesn't have to equal the total number of atoms in the product molecules
C) The identity of the atoms in the reactants has to be the same as the identity of the atoms in the products
D) The physical state of the reactants has to be the same as the physical state of the products

A) The total number of molecules of reactants has to be the same as the total number of product molecules

Explanation:

In chemistry, a chemical equation consists of reactants and products. The reactants are the compounds/substances that chemically combine to give rise to the products. According to the law of conservation of mass, a chemical equation needs to be BALANCED.

A chemical equation is said to be BALANCED when the number of atoms/molecules on the reactant side is equal to that on the product side. In other words, total number of molecules of reactants has to be the same as the total number of product molecules

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.