The attenuation of intensity in a medium follows an exponential law I = I0 e^{-μx}, where μ is the linear attenuation coefficient.

60 kV exceeds the K-shell binding energy (4 keV), so both continuous (bremsstrahlung) and characteristic lines will be produced.

A sustained fission chain reaction requires neutrons to initiate and propagate fission of U-235.

For particles with the same kinetic energy, the heavier particle (alpha) has the greatest momentum and thus the smallest de Broglie wavelength.

The proton mass is approximately 1.007276 u, so the figure corresponds to a proton.

Planck's constant is approximately 6.63 × 10^-34 J·s (option C).

An alpha particle (He2+) capturing a single electron becomes He+ (a helium ion); capturing two electrons would give a neutral helium atom.

Hadrons (which include baryons and mesons) interact via the strong nuclear force, so hadrons is correct.

Bohr radii scale as n^2, so r_4 = 16 × r_1 = 16 × 0.528 Å ≈ 8.45 Å.

Using error propagation ΔA/A ≈ sqrt((ΔL/L)^2+(ΔW/W)^2) and A≈5.45×3.86 gives an uncertainty ≈2.2 (≈0.22 in the OCR's units), matching option D.