Dalton's Atomic Theory:

Introduction:
Dalton's atomic theory, proposed by John Dalton in the early 19th century, was a groundbreaking concept that revolutionized our understanding of the nature of matter. It provided a framework to explain the behavior and properties of different elements and compounds.

Main Points of Dalton's Atomic Theory:
Dalton's atomic theory consisted of several key points, which are as follows:

1. Indivisible Nature of Atoms:
According to Dalton, atoms are indivisible and indestructible particles. They are the fundamental building blocks of matter and cannot be further divided into smaller particles. This concept is often referred to as the "billiard ball" model, where atoms are considered as solid spheres.

2. Atoms of the Same Element are Identical:
Dalton proposed that atoms of the same element are identical in terms of their size, mass, and chemical properties. For example, all carbon atoms are identical, and they differ from atoms of other elements.

3. Different Elements have Different Atoms:
Dalton stated that different elements are composed of different types of atoms. Each element is characterized by its unique atomic structure and properties. For instance, oxygen atoms are distinct from nitrogen atoms.

4. Atoms Combine in Whole Number Ratios:
Dalton observed that when elements combine to form compounds, they do so in specific whole number ratios. This led to the development of the law of definite proportions, which states that a compound always contains the same elements in fixed proportions by mass.

5. Chemical Reactions Involve Rearrangement of Atoms:
According to Dalton, chemical reactions involve the rearrangement of atoms, but no atoms are created or destroyed in the process. This concept is now known as the law of conservation of mass.

Explanation of Option 'A':
The correct answer is option 'A' - "Atoms are indivisible." This statement aligns with Dalton's atomic theory, which proposed that atoms are indivisible and cannot be further divided into smaller particles. Dalton's theory provided the foundation for our understanding of the atomic nature of matter and played a significant role in the development of modern atomic theory. It explained various phenomena and observations related to chemical reactions and the behavior of different elements and compounds. Despite certain limitations, Dalton's atomic theory laid the groundwork for further advancements in the field of atomic physics and continues to be a fundamental concept in chemistry.