28rd

Incorrect spelling, explanation: forming the ordinals from the numbers written in figures such as 8, 28, 38, 48, and so forth, the suffix th is added to them. But the element rd is used for numbers 3, 23, 33, 43, and so on. Besides, this number originated from Old English eahtothe where there was suffix the. And the first known use of this ordinal number was in the late 14th century as eighthe. Nowadays, the only correct form is 28th, not 28rd.

28th

Correct spelling, explanation: 28th is the correct form of the ordinal number that occurs after the 27th. In order to make the ordinals, we add th to the numbers written in figures such as 4, 5, 6… etc. This is the rule but the number 28th consists of twenty and the eighth originated from Old English as eahtotha. Then it appeared in Middle English as eightethe. It has nothing to do with the element rd that is used to make the ordinal number with 3 when we want to indicate that something is in the third position. In view of the foregoing, only 28th is correct.

Definition of 28th:
28th – the ordinal number between 27th and 29th,
I lived here on the 28th floor where there was an amazing view of the city.
My grandfather served in the 28th Louisiana infantry.

28st

Incorrect spelling

28nd

Incorrect spelling