An element is the smallest unit of a compound and retains the compound’s properties. An atom is the smallest unit of an element and retains the element’s properties. Both compounds and elements can have variable composition
The Correct Answer and Explanation is:
Correct Answer:
The statement is incorrect. An element is not the smallest unit of a compound. A compound consists of two or more elements chemically combined in fixed proportions, and its smallest unit is a molecule (for covalent compounds) or a formula unit (for ionic compounds), not an element. An atom is indeed the smallest unit of an element that retains the element’s properties. Also, compounds have fixed composition, not variable composition, whereas mixtures have variable composition.
Explanation
To understand the structure of matter, it is important to distinguish between elements, compounds, and mixtures.
An element is a pure substance made up of only one type of atom. Each element is defined by its atomic number, which is the number of protons in the nucleus of its atoms. The smallest unit of an element that retains the chemical properties of that element is the atom. For example, a gold bar is made up entirely of gold atoms, and each individual gold atom retains all the chemical properties of the element gold.
A compound is a pure substance composed of two or more different elements that are chemically combined in a fixed ratio. For example, water is a compound made of hydrogen and oxygen in a 2:1 ratio. The smallest unit of a compound is a molecule (such as H₂O) or a formula unit (in the case of ionic compounds like NaCl). A compound has its own unique properties, which are often very different from the elements that compose it.
It is incorrect to say that a compound has a variable composition. Compounds always have a fixed composition by definition. If the composition varies, the substance is not a compound but rather a mixture. Mixtures can be either homogeneous or heterogeneous and do not involve chemical bonding between components. For instance, saltwater is a mixture where the ratio of salt to water can vary.
In summary, atoms are the smallest units of elements. Molecules or formula units are the smallest units of compounds. Compounds have fixed composition, and mixtures have variable composition.
