What are the examples of primary standards?

Primary standards are highly pure substances used in quantitative analysis to establish the concentration of solutions. Examples include sodium chloride (NaCl) for ionic strength, potassium hydrogen phthalate (KHP) for acid-base titrations, and silver nitrate (AgNO3) for precipitation reactions. These substances are characterized by their stability, non-hygroscopic nature, and known stoichiometry, making them ideal for calibrating analytical methods.