The atomic number represents the number of protons in an atom. Oxygen has 8 protons, making its atomic number 8.

Solids have both a fixed shape and a fixed volume, unlike liquids or gases. This is a fundamental characteristic of the solid state of matter.

Water is composed of two hydrogen atoms and one oxygen atom, making its formula H2O. The other options either represent incorrect ratios or different compounds.

Oxygen (O2) is a diatomic molecule consisting of only one type of atom, which classifies it as an element. In contrast, water, carbon dioxide, and sodium chloride are compounds because they consist of two or more different elements.

Protons carry a positive charge, which is a basic concept in atomic structure. Neutrons are neutral, electrons have a negative charge, and quarks are sub-components that combine to form protons and neutrons.

The molar mass of CO2 is calculated by adding the molar masses of carbon (approximately 12 g/mol) and two oxygens (approximately 16 g/mol each), which sums to about 44 g/mol. This fundamental calculation is key in stoichiometry.

Charles' Law describes how gases tend to expand when heated, assuming pressure is constant. It establishes a direct relationship between the volume of a gas and its temperature.

Neutralization reactions typically involve an acid and a base reacting to form water and a salt. This is a practical application of the acid-base reaction concept in chemistry.

A covalent bond is formed when atoms share pairs of electrons. This sharing allows each atom to achieve a stable electronic configuration.

Neon has a complete second electron shell with the configuration 1s2 2s2 2p6, which is typical for noble gases. This full valence shell contributes to neon's chemical inertness.

Sublimation is the phase transition in which a substance goes directly from the solid state to the gaseous state without passing through the liquid phase. This concept is important in understanding phase diagrams and molecular behavior.

At 25°C, a neutral solution has a pH of 7, which indicates an equal concentration of hydrogen ions and hydroxide ions. This is a fundamental concept in acid-base chemistry.

Melting of ice requires the absorption of heat from the surroundings, classifying it as an endothermic process. The other processes mentioned release heat, making them exothermic.

At standard temperature and pressure (STP), one mole of an ideal gas occupies 22.4 liters. This relationship is essential for solving problems involving gaseous substances.

A catalyst works by lowering the activation energy, thereby increasing the reaction rate without undergoing permanent chemical change. It is not consumed during the reaction, which makes it distinct from a reactant.

In methane, the carbon atom forms four equivalent bonds by combining one s orbital and three p orbitals to create four sp3 hybrid orbitals. This results in a tetrahedral structure which is a fundamental concept in molecular geometry.

The colors in many transition metal compounds are due to d-d electron transitions, where electrons absorb specific wavelengths of light. This phenomenon explains the various colors observed in coordination complexes and other transition metal compounds.

Le Chatelier's Principle dictates that a system at equilibrium will adjust to counteract any imposed change. When the concentration of reactants is increased, the equilibrium shifts to produce more products in order to reduce the disturbance.

For a reaction to occur spontaneously at constant temperature and pressure, the Gibbs free energy change (ΔG) must be negative. This indicates that the process can proceed without the need for external work.

Ionic compounds have high melting points because the ions in the lattice are held together by strong electrostatic attractions. A large amount of energy is required to overcome these forces, resulting in a high melting point.