Question

How do hydrogen atoms become ionized within an H-II region?

		By absorbing ultraviolet radiation from a nearby star
		By capturing the free electrons within the cloud
		As a result of emitting radiation within the visible light spectrum
		By absorbing radiation within the visible spectrum
		By absorbing thermal radiation from the nearby star

Answer 1

Solution:

By absorbing ultraviolet radiation from a near by star.

HII region is a region of interstellar atomic hydrogen that is ionised. Star formation has taken place recently.

Emission nebula from a central star is responsible for the ionisation. The short lived stars created in these regions emit abundant amounts of Ultra violet light that ionises the surrounding gas.