Dalton's Atomic Theory was able to explain
Law of conservation of mass
Law of multiple proportion
Law of constant composition
Let's recall postulates of Dalton's atomic theory.
(a) Every matter is composed of very minute particles called atoms, which take part in chemical reactions.
(b) Atoms cannot be further subdivided
(c) The atoms of different elements differ from each other in their properties and masses, while the atoms of the same element are identical in all respects.
(d) The atoms of different elements can combine in simple ratios to form compounds. The masses of combined elements represent the masses of combined atoms.
(e) Atoms can be neither created nor destroyed.
Now, let's take a look at all the laws.
⇒ Law of conservation of Mass → matter can neither be created nor destroyed.
⇒ Law of definite proportions → A given compound always contains exactly the same proportion of elements by weight.
⇒ Law of multiple proportions → If two elements can combine to form more than one compound, the ratio of the masses are in the form of small whole numbers.
⇒ These all laws were explained by Dalton using his postulates.
⇒ Allotropy is the property of some chemical elements to exist in two or more different forms, in the same physical state, known as allotropes of these elements.
The concept of allotropy was originally proposed in 1841 by the Swedish scientist. So, it was not there in the theory of Dalton.