Final answer:
Robert Boyle established Boyle's Law, relating the pressure and volume of gases, while Amedeo Avogadro is credited with Avogadro's Law, which joins the volume and number of moles of a gas at constant temperature and pressure.
Step-by-step explanation:
The scientist whose work led to the law that states that the volume of a gas varies with the pressure exerted upon it was Robert Boyle. He articulated what is now known as Boyle's Law, which states that the volume of a given mass of gas varies inversely with the pressure when the temperature is kept constant. Meanwhile, the scientist who argued that matter is composed of atoms, later known as the chemical elements, was Amedeo Avogadro. He advanced a hypothesis in 1811, which became known as Avogadro's Law, stating that equal volumes of all gases, under the same conditions of temperature and pressure, contain the same number of molecules. In honor of Avogadro's contributions, the number of particles in one mole was named Avogadro's number.