In each of the following two questions two statements are given one labelled as the Assertion(A) or Statement I and the other labelled as the reason (R) or statement II. Examine these statements carefully and mark the correct choice as per following instructions
Assertion (A) - Pure water obtained from different sources, such as river, well, spring, sea etc. always contains hydrogen and oxygen in ratio of 1:8 by mass
Reason (R) - Mass of reactants and products during chemical or physical changes is always constant
A. Both A and R are true and R is the correct explanation of A
B. Both A and R are true but R is not a correct explanation of A
C. A is true but R is false
D. A is false but R is true