Question

Law of constant proportion is given by
A.) Thompson
B.) Dalton
C.) Joseph Louis Proust
D.) None of these

Answer 1

Hint: The law of constant proportion gives us an idea about the proportion in which the elements combine to form the compound. We should have an idea about the history behind the development of this law of constant proportion, to answer this question.

Complete step-by-step answer:
The law of constant proportion was proposed by Joseph Louis Proust.
The law of constant proportions states that chemical compounds are made up of elements that are present in a fixed ratio by mass. This implies that any pure sample of a compound no matter the source will always consist of the same elements that are present in the same ratio by mass.
Let us take an example. In case of pure water which consists of hydrogen and oxygen in a fixed mass ratio, there is 0.11 grams of hydrogen and 0.88 grams of oxygen in the ratio 1:8.
Therefore the correct option is Option C.

Additional Information:
There are few limitations of the law of constant proportion. Here are some of them:
The law of constant proportion does not hold true if the different isotopes of the elements are involved in making chemical compounds.
The law is not applicable when elements combine in the same ratio but different compounds are formed.
Where elements exist in the form of different isotopes in its compounds by law does not hold good.

Note: We should know that the law of constant proportion is only applicable if the compound is pure. So a bottle of purified distilled water will have different elements than say water taken from a pond.