The presence of forbidden lines in the spectra of emission nebula indicates that the
A) nebula has a very high temperature.
B) nebula contains large amounts of hydrogen.
C) gas in the nebula has a very low density.
D) dust in the nebula is composed of very small grains of silicates and carbon.
E) nebula is very near a star whose temperature is less than that of the sun.

Question

Quizplus · Accepted Answer

Forbidden lines occur in low-density environments where atoms can remain in excited states long enough to emit these lines, indicating the gas in the nebula has a very low density.

The Presence of Forbidden Lines in the Spectra of Emission