Define an ideal gas.

Hint: There is no gas as an ideal gas, so a hypothetical observation is taken as an ideal gas. There are different gas laws like Charles’s law, Boyles’s law, Avogadro’s law. An ideal gas obeys all these laws. The gas obeys these laws under the same condition of temperature and pressure. Ideal gas equation has been derived from an ideal gas.

Complete answer:
There are various gas laws that can tell the relationship between pressure and volume of gases. Some of which are Boyle’s law that tells that volume of a certain mass of a gas is inversely proportional to pressure at constant temperature. Charles’s law states that volume of a gas is directly proportional to temperature at constant pressure. Avogadro’s law states that equal volume of all gases under similar temperature and pressure contain equal number of molecules.
A gas that obeys all these gas laws under all conditions of pressure and temperature is called an ideal gas. This is a hypothetical observation that means no gas is an ideal gas.
Hence, an ideal gas is defined as a gas that obeys Charles’s law, Boyles’s law and Avogadro’s law under all conditions of pressure and temperature.

Note:
The nature of ideal gas leads to ideal gas equation or equation of states the equation suggests that PV = nRT, where n is the number of moles of a gas with volume V, temperature T, pressure P, R is the universal gas constant that has different values, it can be 8.314 J per Kelvin per mole. It is called the equation of state as the variables like pressure, volume and temperature describe the state of any gas.