Uranium-235 is the readily fissionable isotope used in nuclear reactors and weapons.

Total energy ≈ first ionization (24.6 eV) + second ionization (~54.4 eV) ≈ 79.0 eV.

The block header provides answer hint A; thus 0.023 MeV is taken as the listed correct option.

Protium (a single proton nucleus) has no binding of multiple nucleons, so its mass defect is effectively zero.

Radiation-induced mutations have been used across multiple crops (rice, chickpea, cotton), so the correct choice is 'All of these.'

Gamma rays originate from nuclear transitions, not electronic structure, whereas X-rays, spectral lines and photoelectrons involve electrons.

Decay constant λ = ln2 / T_{1/2} = 0.693 / (5×3600 s) ≈ 3.85×10^{-5} s^{-1}, matching option C.

If remaining after 6 days is 1/8 = 2^-3, then after 10 days remaining = (1/8)^(10/6) = 2^-5 = 1/32, so fraction decayed = 31/32 (option C).

Energy of a photon is given by E = h f, where h is Planck's constant, so Planck's constant is used to compute energy.

For lighter elements the proton-to-neutron ratio is about one, while for some heavier elements the ratio is less than one, so both statements A and C apply.