Question

Q:14 Assertion : During a chemical reaction, the sum of masses of the reactants
and products remains unchanged. This is known as the law of conser
vation of Mass.
Reason: In a pure chemical compound, elements are always present in
a definite proportion by mass. This is known as the Law of Definite
proportions​

Answer 1

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Answer 2

Both Assertion and Reason are correct and Reason is the correct explanation for Assertion

According to the law of conservation of mass, matter can neither be created nor destroyed, so the total quantity of matter, i.e., the total mass, before and after a change, remains the same. So, the mass of the substances, taken together, before and after a chemical change, will also remain same. From this, it can be concluded that any new substance formed during a chemical change is due to the rearrangement of the atoms of the original substance. The number of atoms of each kind remains the same, before and after the chemical change.