Option 1: Composition is variable.

This means that the proportion of elements in a compound can vary. However, this is not a characteristic of a compound. Compounds have a fixed ratio of elements, known as a chemical formula. Each compound has its own unique ratio, and this ratio does not change under normal conditions. Therefore, option 1 is incorrect.

Option 2: All particles of a compound are of only one type.

This is not a characteristic of a compound. In a compound, particles are made up of two or more elements chemically bonded together. These elements combine in specific ratios to form a compound. Therefore, option 2 is correct.

Option 3: Particles of a compound have two or more elements.

This is a characteristic of a compound. Compounds are formed when two or more different elements combine chemically. It is the combination of different elements that gives compounds their unique properties. Therefore, option 3 is incorrect.

Option 4: Its constituents cannot be separated by simple physical methods.

This is a characteristic of a compound. Compounds are formed by chemical bonding, which involves the sharing or transferring of electrons between atoms. Separating the constituents of a compound requires breaking these chemical bonds, which cannot be done by