For Absorption Lines in the Paschen Series of Hydrogen to Be

Multiple Choice

For absorption lines in the Paschen series of hydrogen to be seen in the infrared spectrum of a star (see Section 3-17 of Comins,Discovering the Essential Universe,6th ed.) ,the temperature of its surface must be high enough to excite electrons by collision to the:

A) n = 2 energy level.
B) n = 4 energy level.
C) ionization level.
D) n = 3 energy level.