Rydberg formulated a generalized spectral expression building on Balmer's empirical results, so Rydberg is the correct choice.

The Rydberg formula was developed in the 1890s; among the options, 1894 (B) corresponds to that period.

Photoelectric current (number of emitted electrons) is proportional to the intensity (number of photons) of the incident light.

Lithium bombarded by protons can split into two alpha particles (e.g., Li-7 + p → 2α), so option C is correct.

The Sun's core produces energy by fusing hydrogen nuclei into helium (nuclear fusion), releasing large amounts of energy.

Typical nuclear radii are about 10^-15 m (fermi scale), so option C is correct.

The mean lifetime τ is the reciprocal of the decay constant λ, τ = 1/λ, so option (a).

Removing an electron from a neutral helium atom yields a positively charged helium ion (He+).

The header indicates option A; the listed light-nucleus reactions in A represent fusion processes (answer key in OCR: A).

Wolfgang Pauli formulated the Pauli exclusion principle, so Pauli is the correct choice.