International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

In which state of matter are the intermolecular forces weakest?

1. Solid

2. Liquid

3. Gas

4. Plasma

The correct answer is: Gas

The state of matter where intermolecular forces are weakest is gas. In gases, the molecules are far apart and have high kinetic energy, which allows them to move freely and independently of one another. This high energy overcomes any attractive forces that might exist between the molecules, resulting in very weak intermolecular interactions. Consequently, gas molecules can fill any container they occupy and can expand or compress as needed without being held together by strong forces. In contrast, in solids, molecules are closely packed together in a fixed arrangement, resulting in strong intermolecular forces that hold them in place. Liquids have molecules that are still close together, but they can move past one another, leading to stronger intermolecular forces compared to gases but weaker than in solids. Plasma, while being a state of matter with charged particles, behaves differently and typically exhibits strong forces when contained in specific conditions, often involving ionized gases at high temperatures. Therefore, the nature of gas, with its minimal intermolecular forces, makes it the correct answer.