Suppose that a certain atom possesses only four distinct energy levels. Assuming that all transitions between levels are possible, how many spectral lines will this atom exhibit? 
Definitions:
Obsessive-compulsive Disorder
A mental health disorder characterized by repetitive, unwanted thoughts (obsessions) and behaviors (compulsions).
Repetitive Thoughts
The process of thinking about the same thoughts over and over again, which can be a symptom of various mental health conditions.
Ritualized Behaviors
Actions performed in a prescribed manner that are often symbolic and may be part of religious or cultural practices.
Generalized Anxiety Disorder
A mental health disorder characterized by persistent and excessive worry about various aspects of life, not limited to any specific situation or object.
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