Common mistakes in English sentences

What is the mistake in this sentence, "John was just on time to catch train"?

Answer : Apart from train needing an article ( a train or the the train) it is more usual to say just in time rather than on time.

On time implies that he arrived as expected or scheduled.

In time implies that he arrived before it was too late.

The train didn't leave on time, so he was able to arrive just in time to catch it.