By notation A^Z X, A is mass number (= protons + neutrons) and Z is proton number, so there are Z protons and A−Z neutrons, i.e., option D.

Lead, with high atomic number and density, is most effective at absorbing X-rays.

Per the provided answer key, the selected option is D; this reflects the answer mapping shown in the OCR answer list.

Cosmic radiation originates from outer space and also from radioactive sources in Earth's crust, so 'Both (A) and (B)' best captures the sources.

U-238 + neutron yields U-239 (which can then beta decay toward transuranics), so U-239 is the immediate product.

Mirror nuclei have proton and neutron numbers interchanged between the pair, matching option C.

Bohr radii scale as n^2, so for n=2 the radius is 2^2 = 4 times the first radius, i.e. 4r.

Wave–particle duality in quantum mechanics states that all matter exhibits both particle and wave properties.

Thermal (slow) neutrons commonly induce fission in U-235, producing fragments such as barium and krypton.

An alpha particle has charge 2e, so energy gain = qV = 2e × 200 V = 400 eV.