John Dalton presented the atomic theory in 1803, in which he gave important facts about the nature of matter. According to Dalton’s atomic theory, matter is made up of indivisible particles called atoms. 2. All atoms of an element are identical in size, mass, and chemical properties. 3. Atoms of different elements are different from each other. 4. In chemical reactions, atoms only get rearranged. 5. In compounds, atoms of different elements combine in simple whole-number ratios. 6. Dalton’s atomic theory successfully explained the law of conservation of mass, the law of constant composition (definite proportions), and the law of multiple proportions. Law of conservation of mass – According to the law of conservation of mass, matter can neither be created nor destroyed. Law of definite proportions – This law was given by the French chemist Joseph Proust. According to him, in a compound, the ratio of masses of the elements is always constant. Law of multiple proportions – The law of multiple proportions was given by Dalton in 1803. According to this law, if two elements combine to form more than one compound, then the masses of one element that combine with a fixed mass of the other element are in the ratio of small whole numbers. Therefore, option 4. Particles which can be added to the nucleus of an atom without changing its chemical properties are