Heavy water contains deuterium (²H) in place of ordinary hydrogen.

Compute fission rate from power (250 MW) and energy per fission (200 MeV), multiply by seconds/year and mass per U-235 nucleus; this yields about 9.26×10^1 kg/year, so option B matches.

Work function is an energy, so its unit can be joule or electron-volt; thus both (A) and (B) apply.

Ordinary hydrogen is called protium and is denoted by ^1H, so both B and C are correct.

Classical theory predicts accelerating electrons radiate energy and spiral into the nucleus, so the path would be a spiral.

Maximum electrons up to n=4 = 2*(1^2+2^2+3^2+4^2)=2*30=60, so 60 possible elements.

An atom bomb releases energy via nuclear fission, the splitting of heavy nuclei into lighter fragments with large energy release.

The activity (rate of decay) is proportional to the number of undecayed nuclei and therefore decreases exponentially with time.

The Compton factor h/(m c) has dimensions of length (the Compton wavelength).

Binding energy per nucleon varies systematically with mass number (the binding energy curve), so it depends on the mass number.