I have to identify the error in the following sentence but I don't think there is one :
Christmas holidays start on the 22nd of December.( my teacher said that 'on' is incorrect and that it shouldn't be written but I highly doubt it).
I'd use the "on." I'd say it's okay without it also, but it's certainly not wrong to include it.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.
In British English we usually say "on the 22nd of December", but we write on 22nd December or on 22 December.
Context is always important; labelling is rarely important.
Would it be correct to say : Christmas holiday start the 22nd of December?