Wilson cloud chambers commonly use supersaturated alcohol vapour, which condenses on ions to show particle tracks.

12.5 eV electrons can excite hydrogen up to n=3 (n=4 requires ~12.75 eV), producing transitions 3→2, 3→1 and 2→1 — three wavelengths.

Fusion reaction is a nuclear reaction, not a mode of radioactive decay; positron emission, electron capture and α-decay are decay modes.

The alpha bombardment of N-14 produces O-17 and a proton; the residual nucleus is oxygen (option C).

Louis de Broglie was awarded the Nobel Prize for his work on the wave nature of particles, so the wave nature option is correct.

Iodine-131 is commonly used to treat thyroid disorders and thyroid cancer because it is selectively taken up by the thyroid gland.

λ_max = hc/φ ≈ 1240 eV·nm / 4.0 eV ≈ 310 nm; hence 310 nm is the longest wavelength that can cause emission.

Photoelectric current is proportional to the number of emitted electrons, which depends on light intensity; photon energy affects individual electron energy, not current magnitude.

The answer is taken from the provided answer hint in the block header indicating option A.

A cyclotron accelerates charged particles such as protons to high kinetic energies, commonly producing high-energy protons.