10 days = 4 half-lives, so activity = 1.6 × (1/2)^4 = 1.6/16 = 0.1 curie.

Bohr's quantization condition states that the orbital angular momentum = nh/2π, so angular momentum is quantized.

After one mean life τ, remaining fraction is 1/e ≈ 0.37 so about 63% or roughly 2/3 has disintegrated.

Atomic number is 7 (electrons = 7), so neutrons in isotope B = mass number 16 − 7 = 9, hence option C.

The n=5→2 transition in the Balmer series (Hγ) has a shorter wavelength than n=4→2 and lies in the violet region.

The simplest hydrogen nucleus contains one proton only; other options do not represent hydrogen nuclei.

Implanting a radioactive source inside a tumor to treat it is known as brachytherapy.

Fusion is a nuclear reaction, not a decay mode; typical decay modes include alpha, beta (electron) and gamma emissions.

The ground state is defined as the lowest energy level of the electron; the answer key lists option C.

A deuteron is the nucleus of deuterium, consisting of one proton and one neutron bound together.