Primary cosmic rays are mostly high-energy protons (positively charged particles), so option C is correct.

Carbon dating uses radioactive isotopes (like C-14) to determine ages of archaeological and geological samples.

Stopping potential (largest opposing potential difference) measures the maximum kinetic energy of emitted photoelectrons.

Insulators have the largest band gaps compared to semiconductors and metals (metals have overlapping bands).

The nuclear (strong) force is much stronger than electrostatic force but acts only over very short ranges, so 'stronger and short-range' is correct.

Moseley's law gives the X-ray frequency proportional to (Z − const)^2, i.e., roughly the square of the atomic number.

256→1 is 2^8 reduction, so 8 half-lives × 12.5 hrs = 100 hours.

E = V/d = 2000/0.009 = 2.22×10^5 V/m, q = mg/E ≈ (1.8×10^-14×9.8)/2.22×10^5 ≈ 8×10^-19 C, so n ≈ 8×10^-19/1.6×10^-19 ≈ 5 electrons.

A neutron converting into a proton emits an electron (beta particle) and an antineutrino (beta minus decay).

Bohr's model postulates quantized angular momentum for electrons in orbits.