The OCR answer key in the block marks option A as correct; the field follows the OCR-provided answer.

A nucleon is a constituent of the nucleus, i.e., either a proton or a neutron, so both (a) and (b).

Glashow, Weinberg and Salam were awarded for the electroweak unification, i.e., unifying electromagnetic and weak interactions.

Quantum tunneling explains alpha decay where the alpha particle penetrates the nuclear potential barrier despite classically insufficient energy.

Rutherford's alpha-particle scattering experiments led to the nuclear model, so option B is correct.

To eject K-shell electrons (binding energy 40 keV) and produce characteristic X-rays, the potential must be at least 40 kV.

After four 5-year periods remaining fraction = 0.9^4 = 0.6561, so decayed ≈ 1 - 0.6561 = 0.3439 ≈ 34.4% (option D).

In nuclear physics the excitation function plots reaction cross-section as a function of incident particle energy.

Stern–Gerlach shows a beam of electrons splits into two discrete spots corresponding to spin-up and spin-down, indicating electrons are spin-1/2 fermions with two possible spin orientations.

The described fact is known as the whole number rule regarding isotopic masses.