Least energetic Lyman photon is n=2→1: λ = 1/[R(1−1/4)] = 4/(3R) ≈ 1.215×10⁻7 m ≈ 122 nm.

Answer taken from block answer hint (B) as provided in the OCR header for this block.

A unit cell is the smallest repeating three-dimensional unit that builds up the crystal lattice.

Curie is a unit used to measure radioactivity (activity), so option C is correct.

An alpha particle (helium nucleus) becomes a neutral helium atom by capturing two electrons, so option B is correct.

Odd-A nuclei typically have half-integer total spin, so half-integral spins is correct.

100/12.5 = 8 half-lives, so remaining = 256 × (1/2)^8 = 256/256 = 1.00 gm.

Elasticity is the property that allows a body to regain its original shape after removal of deforming forces.

Relativistic mass increases with speed and would grow without bound as v approaches c, so it is greater than the rest mass.

Binding energy is the energy required to separate a nucleus into its constituent nucleons.