What does concentration refer to in chemistry?

Concentration in chemistry refers to the amount of a substance present in a specific volume or defined space of a solution. It quantitatively measures how much solute is dissolved in a solvent at any given time, which is crucial for understanding the behavior of substances in chemical reactions.

When discussing concentration, we often encounter various units such as molarity (moles of solute per liter of solution) or mass/volume percent. This measurement is fundamental in stoichiometry, allowing chemists to predict the outcomes of reactions, control reactions, and prepare solutions with desired properties.

The other options are related to different aspects of chemistry but do not define concentration. Temperature pertains to thermal energy, pH level measures the acidity or basicity of a solution, and the physical state refers to whether a substance is solid, liquid, or gas. Each of these plays an important role in chemical behavior but does not directly describe what concentration means.