1)Law of conservation of mass :- in all physical and chemical charges, the total mass of products in same as that of react reactants.

Mass of NaCl is = 6.0 + 1.825 = x + 4.9

So x = 2.925 g

Note:- so in nuclear reactions, mass is converted to energy. So modified law is “ mass and energy of a system remains constant”.

This has given by Antoine Lavoisier (1789)

2)Law of constant composition:- by Joseph Proust a pure compound always consists of same elements combined together is a fixed ratio.

eg. H₂O from any source always contains 2g H₂ and 16 g oxygen by weight in 1 mole of it.

3)Law of multiple proportion:-by Dalton (1803) when two elements combine together to form many compounds then the masses of one elements are in the ratio of small whole numbers.

eg. Hydrogen and oxygen combine to form H₂O and H₂O₂ then with 2g of Hydrogen, the masses of oxygen combined are 16g and 32g, so ratio is 16 : 32,    1 : 2

4)Gay Lussac’s law of gaseous volumes:- (1808)

It states that “ when gases combine or are produced in a chemical ratio. They do so in a simple ratio by volume provided all gases are at same temperature and pressure”

eg.

5) Avogadro’s law:- (1811) it states that “equal volume of all the gases at same temperature and pressure contain equal no. of molecules” his work was published in Journal de physique.