Question

A balance chemical equation is in accordance with:
A. Avogadro’s law
B. Law of constant proportion
C. Law of conservation of mass
D. Law of gaseous volumes

Answer 1

Hint: We know that in balanced chemical equations, we have equal numbers of atoms for all the elements which take part in the reaction on both the sides.

Complete answer
We might encounter various chemical changes taking place all around us. These are also called chemical reactions. The examples can include from burning incense sticks in temples to cooking gas in kitchens. While expressing these chemical reactions, detailed description might get confusing and tedious so we can use word equations or the best option is chemical equations where we use the universally accepted chemical formulae for all the involved species. For example, reaction of ${H_2}$ and ${O_2}$ gases to give water can be shown by the following chemical equation:
${H_2} + {O_2} \to {H_2}O$
However, if we look at the mass of the reactants and products, it might appear that some mass has been lost:

$H_2$	$+$	$O_2$	$\longrightarrow$	$H_2O$
2 g		32 g		18 g

We know for fact, that it is not possible as it has been established that matter can neither be destroyed nor created. In the words of Dalton, atoms can be reorganized during a chemical reaction but not created or destroyed. This is known as the law of conservation of mass for mass remains constant before and after the reaction.
To cater to this, we have balanced chemical equations that follow the law of conservation of mass as the number of atoms for each element is equal before and after the reaction. For the above given example, we wrote only skeletal chemical equation that doesn’t follow the law of conservation of mass but when it is balanced as shown below:

$2H_2$	$+$	$O_2$	$\longrightarrow$	$2H_2O$
4 g		32 g		36 g

We can see that the number of $H\;{\rm{and}}\;O$ atoms are same $\left( {4H\;{\rm{and}}\;2O} \right)$ respectively as well as mass is conserved.

Hence, the correct option is C.

Note:
We have to keep in mind that all the other laws given as options are related to a given matter/compound/molecule. Dalton's atomic theory was also based on the Law of Conservation of Mass.