The most common isotope of natural uranium has mass number 238, so 238 is correct.

Using φ=hc/λ_threshold and E=hc/λ_incident gives KE≈3.05 eV, yielding v≈1.04×10^6 m/s (option B).

Deflection of alpha particles by thin foils arises mainly from electrostatic repulsion between the positively charged alpha particle and the positive nucleus.

Shear stress deforms a body by changing its shape without primarily changing its volume.

The block's OCR answer key marks option A as correct; the response follows the OCR-provided answer.

The OCR answer hint marks option A; the closest approach is found by equating kinetic energy to Coulomb potential, yielding the value shown in option A as per the text.

The continuous X-ray spectrum arises from bremsstrahlung ('braking radiation'), produced when electrons decelerate in the target.

Option A shows a plausible light-nuclei capture releasing MeV energy and was indicated as correct in the block answer hint.

The Balmer series falls in the visible region of the electromagnetic spectrum; the OCR indicates option A selected.

The block header provides the answer key; for identical equal-mass particles a common relation used is θ_lab = 2 θ_cm as given in option A.