A neutral atom has equal numbers of protons and electrons, so option (d) is correct.

Emission of an electron (beta minus) converts a neutron to a proton, leaving mass number unchanged and increasing atomic number by one.

Leptons (e.g., electrons, muons) are spin-1/2 particles; mesons are bosons with integer spin.

In Bohr model r ∝ n^2 and frequency f ∝ 1/n^3; radii ratio 1:9 implies n ratio 1:3 so frequency ratio is 27:1.

The deuteron's binding energy is about 2.23 MeV, matching the OCR-marked option A.

A moderate potential difference (on the order of hundreds of volts) is applied across the chamber to remove unwanted ions without disrupting tracks.

Bohr's model did not account for fine structure caused by relativistic and spin effects, so it couldn't fully explain fine structure.

Using the given collision parameters for carbon and the provided formula context, the calculated average energy loss corresponds to option C.

Both alpha particles and gamma rays are capable of causing ionization in air, although their ionization densities and mechanisms differ.

In the Bohr model for Coulomb potential, potential energy = -2 × kinetic energy, so the ratio is -2.