State the ideal gas law and the conditions under which real gases behave ideally.

• A. PV = nRT; real gases behave ideally at high pressure and low temperature where intermolecular forces are strong.
• B. PV = nRT; real gases behave ideally at low pressure and high temperature where intermolecular forces and molecular volumes are negligible.
• C. P + V = nRT; ideal conditions require high density.
• D. PV = n^2RT; ideal gases behave ideally at any condition.

Answer: (B)

The main idea is that the ideal gas law PV = nRT describes a hypothetical gas where molecules do not occupy volume and do not interact with one another, so pressure times volume depends only on temperature and amount of substance. Real gases behave like this only when those simplifying assumptions hold well enough: the molecules are far apart and moving rapidly, so intermolecular forces are minimal and the actual molecular size becomes negligible compared to the container.

That happens at low pressure and high temperature. Under those conditions, collisions are mostly elastic and the space taken by the molecules themselves is small compared to the container volume, so PV ≈ nRT holds true. If you crank up the pressure or lower the temperature, molecules are closer together and their sizes plus attractions matter, causing deviations from the ideal law.

So the statement that PV = nRT describes the ideal gas law, and real gases behave ideally at low pressure and high temperature where intermolecular forces and molecular volumes are negligible. The other options either give an incorrect equation or propose conditions that would not yield ideal behavior.