Question

A balanced chemical equation is in accordance with which one of the following laws given below?
A) Law of conservation of energy
B) Law of conservation of mass
C) Law of constant proportion
D) Law of multiple proportions
E) None of these

Answer 1

A balanced chemical reaction is a reaction in which the number of atoms of reactant taking part in the reaction is always equal to the number of atoms of the product. In other words, if A produces the $\text{ }{{\text{A}}_{\text{2}}}\text{ }$ , then the number of atoms of the A should be equal on either side of the reaction. i.e.
$\text{ 2A}\to \text{ }{{\text{A}}_{\text{2}}}$
The balanced equation is expressed in terms of moles of the reactant of atoms and product.

Complete step by step answer:
A chemical reaction can be expressed in terms of change in the composition of the reactants and product. It says that a certain amount of reactant undergoes the reaction to produce a certain amount of product. The reactant and product which are utilized and formed are measured in terms of ‘moles’. Since the mole is a concept that can be applied to any state of matter.
We know that moles are the ratio of the mass of solute to the molar mass. That is, the mass of the reactant is completely utilized to form the product and sub product. The mass on either side of the reaction arrow is always the same.
That is, every chemical reaction obeys the law of conservation of mass. According to which, the matter neither be created nor destroyed but can be changed from one form to another (reactant to product) therefore, the number of atoms of each element in the reactant side is always equal to the number of moles of atoms on the product side. such reactions are called the balanced chemical reaction.
Let's consider the chemical reaction to yield a table salt, sodium chloride $\text{ NaCl }$from sodium metal, and chlorine gas. The unbalanced reaction is as follows:
$\text{ Na (s) + C}{{\text{l}}_{\text{2}}}\text{ (g) }\to \text{ NaCl (s) }$
Here, we have two chlorine atoms from the chlorine molecule at the reactant side. This is indicated by the subscript 2 on the chlorine. On the product side, we have salt $\text{ NaCl }$where the ratio of sodium to chlorine is$\text{ 1:1 }$, therefore, there is a single atom of chlorine to the product side.
We need to add the coefficients to $\text{ NaCl }$on the product side.
Let's balance the reaction by adding 2 as the coefficient in front of$\text{ NaCl }$. We have,
$\text{ Na (s) + C}{{\text{l}}_{\text{2}}}\text{ (g) }\to \text{ 2NaCl (s) }$
Here, the two chlorine atoms are on the reactant and product side of the reaction. However, now we have one atom of sodium on the reactant side and 2 on the product side. Thus, add 2 as the coefficient in front of sodium in the reactant side.
We have,
$\text{ 2Na (s) + C}{{\text{l}}_{\text{2}}}\text{ (g) }\to \text{ 2NaCl (s) }$
Here, there are two sodium atoms and two chlorine atoms on both sides of the reaction. The number of moles of atoms is equal and thus the above reaction is balanced.
The balanced chemical reactions are following the law of conservation of mass.

Hence, (B) is the correct option.

Note: Note that, never try to balance the equation by changing the subscript of the molecule. The subscript is unique and has characteristics of a specific molecule, which decides the number of atoms in molecules, the stability, reactivity, etc. The changing the subscript would result in the new molecules which may lead to the undesired product. Thus, always balance the reaction by considering the coefficient in front of atoms.