it was a jungle out there vs. it was mayhem

[Vladimir13]

English Language Proficiency Tests, Advanced Level

ESL/EFL Test #527 "English Slang Idioms (111)", question 2

"I went to see the presidential candidate speak in our town and let me tell you, it was a ......... out there. You couldn't hear the man speak, fights were breaking out, everyone was yelling and cussing at each other and someone's car was flipped over," Lisa told Elizabeth.

(a) mayhem
(b) jungle
(c) meeting of the minds
(d) moratorium

English Language Proficiency Tests, Advanced Level

ESL/EFL Test #527 "English Slang Idioms (111)", answer 2

"I went to see the presidential candidate speak in our town and let me tell you, it was a jungle out there. You couldn't hear the man speak, fights were breaking out, everyone was yelling and cussing at each other and someone's car was flipped over," Lisa told Elizabeth.

Correct answer: (b) jungle

Your answer was: incorrect
"I went to see the presidential candidate speak in our town and let me tell you, it was a mayhem out there. You couldn't hear the man speak, fights were breaking out, everyone was yelling and cussing at each other and someone's car was flipped over," Lisa told Elizabeth.
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Hi Teachers,

Tell me please why "mayhem" in the sence of "violent or damaging disorder; chaos" is not correct here?

Thank you,
Vladimir.
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My little horse must think it queer...

[Beeesneees]

You would have to say
It was mayhem
not
it was a mayhem.

The inclusion of the indirect article indicates that mayhem cannot be used, as 'mayhem' is uncountable.
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"Inside every old person is a young person wondering what happened."
Terry Pratchett