While some rare processes emit neutrons, typical radioactive decay emits α, β and γ; neutrons are not commonly emitted in ordinary radioactive decay.

A proton consists of two up quarks and one down quark, uud, so option (d).

Radioactive emission generally either removes excitation energy or leads to a more stable nuclear configuration, so either (a) or (b) is correct.

Decay from a heavier nucleus to one 2 mass units lighter (e.g., Ra → Rn with mass change of 4) typically indicates emission of an alpha particle.

The block provides option B as the answer in its OCR answer hint; Compton scattering treatment assumes electrons approximately free and initially at rest.

An alpha particle (helium nucleus) has mass roughly 7000 times that of an electron.

A beta-minus particle (electron) emission results from a neutron converting into a proton (neutron → proton + electron).

The Nagasaki bomb (Fat Man) used plutonium-239 as its fissionable material.

An electron has much less mass than either a proton or a neutron, so the option stating it is smaller than a proton or neutron is correct.

A body-centered cubic (BCC) unit cell has one atom at each corner (1/8 × 8 =1) plus one in the center, giving 2 atoms per unit cell.