Cadmium rods absorb neutrons and are used to control or halt a chain reaction in a reactor, so cadmium rods are correct.

The OCR shows a marker next to option C; the mass defect is the difference between constituent particle masses and the actual atomic mass, so option C is correct.

For hydrogen-like ions wavelength scales as 1/Z^2; for He+ (Z=2) the wavelength is 1/4 of 20,397 ≈ 5,099 units.

A whole-body dose of about 10 rem (0.1 Sv) typically does not cause rapid death but can produce detectable changes in blood parameters.

Maximum kinetic energy follows Kmax = hν − φ, so it depends on the frequency of the incident radiation.

The ground-state (first Bohr orbit) energy of hydrogen is -13.6 eV.

1/16 = (1/2)^4 so 1 day = 4 half-lives ⇒ half-life = 24 hours/4 = 6 hours.

Total electrons up to shell n is 2(1^2+2^2+3^2+4^2)=2×30=60, so option B is correct.

An electron accelerated through potential difference V gains kinetic energy equal to eV.

Neutrons are neutral so electrostatic force is negligible; gravitational and the nuclear strong force can attract neutrons, making C correct.