Statement A: Atoms can exist independently.

This statement is false. Atoms cannot exist independently in nature. They are the building blocks of matter and combine with other atoms to form molecules or compounds. Atoms are composed of protons, neutrons, and electrons. The protons and neutrons are located in the nucleus of the atom, while the electrons orbit around the nucleus. The number of protons determines the atomic number of an atom, which in turn determines the element to which the atom belongs.

Atoms have a strong tendency to bond with other atoms to form stable molecules or compounds. This bonding can occur through various types of chemical bonds such as ionic bonds, covalent bonds, or metallic bonds. These bonds are necessary for atoms to achieve a stable electron configuration, which is more energetically favorable than having unpaired electrons.

Statement B: The law of constant proportions is applicable only to pure chemical compounds.

This statement is true. The law of constant proportions, also known as the law of definite proportions, states that in a pure chemical compound, the elements are always present in definite and fixed proportions by mass. This means that regardless of the source or method of preparation, a pure compound will always contain the same elements in the same ratio by mass.

For example, water (H2O) will always consist of two hydrogen atoms for every one oxygen atom, regardless of whether it is obtained from a natural source or synthesized in a laboratory. Similarly, carbon dioxide (CO2) will always have one carbon atom for every two oxygen atoms. This law was first proposed by the French chemist Joseph Proust in the late 18th century and has been verified by numerous experiments and observations.

However, the law of constant proportions does not apply to mixtures, as the composition of a mixture can vary. In a mixture, the different components can be present in different proportions and can be separated by physical means such as filtration or distillation. Therefore, the law of constant proportions is only applicable to pure chemical compounds.