(A) all the time.
(B) never.
(C) until they land on the nucleus.
(D) only when changing orbit.
(A) all the time.
No.
Atoms are usually stable.
(B) never.
No. --- Bohr's model does explain
the radiation emitted by Hydrogen.
(C) until they land on the nucleus.
No. --- That never happens
and Bohr's model forbids it.
(D) only when changing orbit.
Yes.
During a "quantum jump".