Above threshold, higher photon frequency increases the kinetic energy of emitted electrons, not the current (which depends on intensity).

Baryons (like protons and neutrons) have masses comparable to or greater than the proton; mesons are generally lighter and positron is a lepton.

Zirconia is a ceramic, not a polymeric solid; polythene, nylon, and synthetic rubber are polymers.

Iron has the highest binding energy per nucleon, indicating maximum nuclear stability; the OCR answer key marks Iron.

Bohr radius scales inversely with orbiting particle mass, so a particle 207 times heavier gives a radius smaller by factor 207, i.e., r_H/207.

After two half-lives (4 minutes) the remaining fraction is (1/2)^2 = 1/4.

Einstein's relation E = mc^2 equates mass times c^2 to energy, so option D is correct.

Planck introduced the idea that energy is quantized in discrete packets called quanta.

The required energy to remove the most loosely bound electron is called the ionization potential (ionization energy), so option C is correct.

An atom is composed of three primary subatomic particles: protons, neutrons, and electrons.