Correct spelling, explanation: 22nd is an ordinal number, whose full form is twenty-second. The short form 22nd is much more common than the full form and is usually used in dates, entry lists, etc. It is worth noticing that as the ending, which makes 2 an ordinal number is -nd, which gives 2nd, the same happens with 22 and the ordinal number is 22nd.

Definition of 22nd:
1. number (ordinal) – a short form of twenty-second, a number which appears between 21st and 23rd,
I’ve got an appointment at my dentist’s on the 22nd of March and I don’t know how I will handle my tooth pain for so long.

Expressions with 22nd:
A few common expressions with 22nd are: 22nd birthday, 22nd position, and 22nd of December.
We’re going to prepare for him a surprise party for his 22nd birthday so don’t tell him anything.
When I heard that he finished the marathon in the 22nd position I felt really proud of him.
22nd of December is a little bit too late for looking for a Christmas tree, isn’t it?

Incorrect spelling, explanation: creating ordinal numbers in English is confusing as a number of users have a problem with the correct ending. Most ordinal numbers have the -th ending, e.g. fifth, tenth, etc., but the first three numbers are different as they are the 1st, 2nd, and 3rd. The same happens with 22, which as the ordinal number is 22nd. Some users forget about it and spell 22nd as 22st, which is wrong.

Incorrect spelling

Incorrect spelling