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Hint: For this question we must have the knowledge for the first ever theory for the existence of atoms. That time the subatomic particles were not known and the thought of having the subunits of matter was put forward.
Complete step by step solution:
In 400 B.C. the Indian and Greek philosophers proposed the existence of atoms as the subunit of matter. They considered atoms as fundamental building blocks for matter. According to them, when we divide atoms continuously again and again. We ultimately get the smallest particles out of which matter is made up of. They termed that smallest particle as an atom. During that time electrons, protons and neutrons were not discovered and the technology was not developed enough to study about them.
This was assumed true for a very long period of time until the 18th century. After that various experiments and we got the famous Dalton’s atomic theory came in the early 19th century.
Hence the correct option is A.
Additional information:
The postulates of Dalton’s atomic theory are:
All the matter is made up of tiny particles called atoms.
An atom of a specific element is similar in shape, size, mass etc. and atoms of different elements differ in shape size and mass etc.
Atoms can neither be created nor be destroyed.
Atoms of different elements combine with each other in fixed ratios that too should be the whole number to form chemical compounds.
Note: The electrons, protons and neutrons are subatomic particles of atoms. The discovery of electrons was done by J.J, Thomson in 1897. Protons were discovered by Rutherford in 1919 and neutrons were discovered by Chadwick.
Complete step by step solution:
In 400 B.C. the Indian and Greek philosophers proposed the existence of atoms as the subunit of matter. They considered atoms as fundamental building blocks for matter. According to them, when we divide atoms continuously again and again. We ultimately get the smallest particles out of which matter is made up of. They termed that smallest particle as an atom. During that time electrons, protons and neutrons were not discovered and the technology was not developed enough to study about them.
This was assumed true for a very long period of time until the 18th century. After that various experiments and we got the famous Dalton’s atomic theory came in the early 19th century.
Hence the correct option is A.
Additional information:
The postulates of Dalton’s atomic theory are:
All the matter is made up of tiny particles called atoms.
An atom of a specific element is similar in shape, size, mass etc. and atoms of different elements differ in shape size and mass etc.
Atoms can neither be created nor be destroyed.
Atoms of different elements combine with each other in fixed ratios that too should be the whole number to form chemical compounds.
Note: The electrons, protons and neutrons are subatomic particles of atoms. The discovery of electrons was done by J.J, Thomson in 1897. Protons were discovered by Rutherford in 1919 and neutrons were discovered by Chadwick.
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