Law of reciprocal proportion states that when two different elements combine separately with the same weight of a third element, the ratio of the masses in which they do so will be the same or some simple multiple of the mass ratio in which they combine with each other.

Different proportion of oxygen in the various oxides of nitrogen proves the law of multiple proportions, which states:

In $PH _3$, the ratio by weight of $P:H=31:3$

The Law of Multiple Proportions : It was given by Dalton. When one element combines with the other element to form two or more different compounds, the mass of one elements, which combines with a constant mass of the other, bear a simple ratio to one another.
$N _2O, NO, NO _2$
The law of reciprocal proportions states that, when two different elements separately combine with a fixed mass of a third element, the proportions in which they combine with one another shall be either in the same ratio or some multiple of it. For example, sulphur and carbon both form compounds with hydrogen. In methane 12g of carbon react with 4g of hydrogen. In hydrogen sulphide, 32g of sulphur react with 2g of hydrogen (i.e. 64g of S for 4g of hydrogen). Sulphur and carbon form a compound in which the C: S ratio is 12:64 (i.e. $CS _2$).

A) French chemist A. Lavoisier is called the father of chemistry and proposed the law of conservation of mass. (True)

The weight ratio of two elements A and B which combine with the fixed weight of C separately is either the same or some simple whole number multiple of the weight ratio in which A and B combine together. This statement explains the Law of reciprocal proportion.
For example, 23 g of $Na$ combines with 35.5 g of $Cl$ and 1 g of $H$ to form $NaCl$ and $NaH$. Hence, 35.5 g of $Cl$ and 1 g of $H$ will combine to form $HCl$.

In experiment $A-$ Oxide of $Pb=8.92g$

Law of reciprocal proportion was proposed by J. Richter according to which If two different elements combine separately with the same weight of a third element, the ratio of the masses in which they do so are either the same or a simple multiple of the mass ratio in which they combine.

Law of Equivalent Proportion and Law of Permanent Ratios are the other names for the Law of Reciprocal Proportion.

Its easy as $NH _3 : N _2 : H _2$ IS 2:1:3 As $NH _3$ is 40 ml hence form 60 ml of h2 and 20 ml of n2

Law of Reciprocal proportions:-

Law of reciprocal proportions is also called as the law of equivalent proportions and law of permanent ratios.

The ratio of Masses of oxide of $Cu$ to $Cu$,

Jeremias Richter (Jeremias Benjamin Richter) was a German chemist. He proposed the law of Reciprocal proportions in $1792$.

The law of reciprocal proportions is one of the basic laws of stoichiometry. It relates the proportions in which elements combine across a number of different elements. A simple statement of the law is:

 Element A combines with element B and also with C, then, if B and C combine together, the proportion by weight in which they do so will be simply related to the weights of B and C which separately combine with a constant weight of A.

Hydrogen combines with Oxygen to form ${ H } _{ 2 }O$

$2:16\\ 1:8$

Phosphorous combines with Oxygen to form ${ P } _{ 2 }O _{ 5 }$

$62:80\\ 31:40\\ $

Phosphorous combines with Hydrogen to form $P{ H } _{ 5 }$

$31:5\\ \cfrac { 31 }{ 40 } \times \cfrac { 8 }{ 1 } =\cfrac { 31 }{ 5 } $

According to Gay-Lussac's Law, the ratio between the volumes of reactants and products can be expressed in simple whole numbers.