请教一道化学题

zasdzccUID: 173579

When excited electron cascade to lower energy levels in an atom,
% l9 Y% h. a+ n8 d2 ^) o+ i(A) visible light is always emitted
( d7 H8 [( V! N) ~4 B( k(B) the potential energy of the atom increases
! M" v4 v. a0 w. h% O. O2 W(C) the electron always fall back to the first energy level
(D) the electron fall discriminately to all levels.
+ H( i# Y( U* Z8 d, W(E) the electron fall back to the lowest unfilled energy level
" l2 i& o* V- M' ?5 C: c/ T# jAnswer(E).
请问为何选E不选A？electron cascade是甚么.Thanks.

imongUID: 140258

电子跃迁。

: D8 E' L/ U6 R7 k) J. s( a不一定是visible light啊。能级差得不大不就不visible了么。