Incorrect spelling

11st

Incorrect spelling, explanation: this form is incorrect because we add suffix -st to ordinal numbers ending with first. Here, eleven has got ordinal form eleventh, therefore it ends with -th. This is why 11th is the correct way we write this ordinal number.


Correct spelling

11th

Correct spelling, explanation: this ordinal number should be written as 11th because they don’t pronounce it with first at the end (which would then indicate -st suffix), but we pronounce it eleventh, so with -th at the end. This is the reason for writing it as 11th, not 11st.

Definition of 11th:
numeral, the ordinal number between 10th and 12th
Jerry is Betty’s 11th husband! Can you believe it?
I wanted to be at least 10th in the marathon but unfortunately, I came 11th.


Incorrect spelling

11nd

Incorrect spelling

Incorrect spelling

11rd

Incorrect spelling