5th

Correct spelling, explanation: 5th comes after 4th and before 6th and the -th ending makes it an ordinal number. Most ordinal numbers are formed as 5th, which is by adding the -th to the number. However, numbers 1, 2, and 3 are exceptions as their ordinal numbers are 1st, 2nd, and 3rd.

Definition of 5th:
1. number (ordinal) – appears between 4th and 6th, the full, written form is fifth,
The expectations were huge but he finished the race in the 5th position, which was disappointing.

Expressions with 5th:
1. I take the 5th (Amendment) – an expression used when you don’t want to answer the question because you find it uncomfortable,
‘Which sister do you find more attractive, John?’ ‘Sorry, I take the 5th on that.’

5rd

Incorrect spelling, explanation: the first three ordinal numbers are 1st, 2nd, and 3rd, which causes some confusion among English users when it comes to forming further ordinal numbers. For example, they use the form 5rd instead of 5th while the rule says that we simply add the -th ending to a number, e.g. 4th, 5th, 6th, etc.

5st

Incorrect spelling

5nd

Incorrect spelling