Read the following passage and answer the questions 

Atoms are the fundamental building blocks of matter. Each atom consists of a nucleus, containing protons and neutrons, surrounded by electrons in various energy levels or orbitals. The number of protons in the nucleus, known as the atomic number, defines the element. Atoms can join together to form molecules, which are groups of two or more atoms bonded together. These bonds can be covalent, where atoms share electrons, or ionic, where electrons are transferred from one atom to another, resulting in positively and negatively charged ions that attract each other. The arrangement and interactions of atoms and molecules determine the physical and chemical properties of substances. For example, water (H₂O) is a molecule composed of two hydrogen atoms and one oxygen atom, with a unique set of properties essential for life. Understanding atoms and molecules is crucial for fields ranging from chemistry and physics to biology and materials science, as they explain the nature of chemical reactions, the structure of compounds, and the behavior of different materials.