The scientist who discovered the zig-zag movement of gas molecules is

Analyze the question: It asks who discovered the random, zig-zag movement of particles. This is known as Brownian motion.

Explain the concept: In 1827, the Scottish botanist Robert Brown observed pollen grains suspended in water moving in a random, jerky, zig-zag path under the microscope. The movement is caused by the particles being constantly bombarded by fast-moving, invisible molecules of the surrounding medium (liquid or gas). The same happens with smoke particles in air, which is where the "gas molecules" link comes from. This random motion gave strong evidence for the kinetic theory of matter.

Check the options:

• A. Brownian: Brownian motion is the zig-zag random movement of particles. The option names the scientist by the motion's name (Brown), so it fits.
• B. Dalton: proposed the atomic theory and the law of partial pressures.
• C. Gay-Lussac: law of combining volumes of gases and the pressure-temperature law.
• D. Graham: law of diffusion/effusion of gases (rate is inversely proportional to the square root of density or molar mass).
• E. Newton: laws of motion and gravitation.

Answer: The zig-zag movement is Brownian motion, so the correct option is A. Strictly speaking, the scientist's name is Robert Brown, and "Brownian" is the adjective form, but it is clearly the intended choice.

Exam tip: Link names to ideas:

• Brown → zig-zag random motion
• Graham → diffusion
• Dalton → atoms and partial pressure
• Gay-Lussac → combining volumes