Nuclear fusion is the process where two light nuclei combine to form a heavier nucleus, releasing energy.

Ionisation energy from level n is 13.6/n^2; for n = 2 this gives 13.6/4 = 3.4 eV, so option C is correct.

In the context of photoelectric effect apparatus, symbols like I1 and I2 typically denote measured photoelectric currents under different conditions.

Pair production converts photon energy into particle pairs, i.e., it materializes energy into matter.

The OCR header indicates option A (2,182 me V) as the rest mass given for Aº in the text.

Energy -3.4 eV corresponds to n=2, so angular momentum L = nħ = 2 × 1.055×10^-34 ≈ 2.11×10^-34 Js.

The Q-value is the difference between initial and total kinetic energies of products; the provided energies yield a Q ≈ 7.49 MeV, corresponding to option A.

Nuclear forces act over very short distances (short range), so option C is correct.

The block header identifies option D as the answer; the OCR text links the small electron-hole formation energy to detector sensitivity per the provided key.

Iodine molecules produce molecular band absorption features when white light passes through their vapor, giving a band absorption spectrum.