Incorrect spelling, explanation: this form is incorrect because the twelfth ends with th, not nd, so 12nd doesn’t make sense. When writing ordinal numbers we add the sound that the word form ends with. This applies to all ordinal numbers, so twenty-second is 22nd and forty-first is 41st, etc.

Correct spelling, explanation: 12th is the correct form because we write the word form as twelfth. As you can see there is a th sound at the end. Therefore, as with all other ordinal numbers, we add such suffixes to the number form. This happens with all ending sounds, for example, second = 2nd or fifty-sixth = 56th. This is why 12th is correct and not 12nd.

Definition of 12th:
numeral, the ordinal number between 11th and 13th
I come from a large family – I am my parent’s 12th child!
She had to wait for a little because she was 12th on the list.

Incorrect spelling

Incorrect spelling