It is NOT possible to determine exactly and simultaneously the position and momentum of a particle. This statement is known as the

Step 1: Analyze the question The statement says we cannot know a particle's exact position and exact momentum at the same time. We need to match this to the correct named principle.

Step 2: Explain the concept This is the Heisenberg uncertainty principle. It states that the more precisely you measure a particle's position (Δx), the less precisely you can know its momentum (Δp), and vice versa:

Δx · Δp ≥ h/4π

This is not due to faulty instruments. It is a fundamental property of nature at the atomic and subatomic scale, arising from the wave-like behaviour of matter.

Step 3: Check each option

• A. Compton effect: The increase in wavelength of X-rays when they scatter off electrons. It is evidence for the particle nature of light, not about uncertainty.
• B. de Broglie's laws: Every moving particle has an associated wavelength, λ = h/mv. This is about matter waves, not simultaneous measurement.
• C. Franck-Hertz experiment: Showed that atoms absorb energy in discrete amounts, which supports quantized energy levels.
• D. Heisenberg's uncertainty principle: Exactly matches the statement.
• E. Wave-particle paradox: Refers to the dual nature of matter and light, not the limit on measuring position and momentum together.

Step 4: Answer The correct option is D. Heisenberg's uncertainty principle.

Exam tip: Whenever you see "position and momentum cannot be known simultaneously" (or "energy and time"), think Heisenberg. Remember: Heisenberg = Hazy about where something is and how fast it's moving at the same time.