hello. Thanks a lot for your help.I have a problem whit meaning of the above word. single what means?
for example in this sentence:
If the frequency of the applied field is comparable to the collision frequency, electrons may accelerate and decelerate between collisions, and the model treating the metal as a single gas loses the validity (Jackson 1998).

the metal as a single gas loses the validity
فلز به عنوان یک گاز تک مولکولی [اتمی] دیگر معتبر نیست.