Radio Waves of 21-Cm Wavelength Originate from Which Component of the Interstellar

question 93

Multiple Choice

Radio waves of 21-cm wavelength originate from which component of the interstellar medium?

• A) cool, neutral atomic hydrogen
• B) cold molecular hydrogen, H₂
• C) cool carbon monoxide, CO
• D) hot, ionized atomic hydrogen

---

Definitions:

Neutral Stimulus

A stimulus that initially produces no specific response other than focusing attention, until it is paired with an unconditioned stimulus.

Classical Conditioning

A learning process in which a neutral stimulus becomes associated with an inherently meaningful event or stimulus, eliciting a conditioned response.

Turned Off

A colloquial term describing a lack of interest or a state of disinclination towards something.

Memory

The faculty by which the mind stores and remembers information, critical to learning and the formation of identity.