My School Slice for the Day

Here's what I posted to my class writing challenge today:

Today I'm going to try something new. As a special thank-you to everyone who has gone the extra mile and posted and replied to this writing challenge, I'm going to put a little puzzle into my Slice of Life. If you can solve the mystery and tell me the answer tomorrow, you will receive the reward of a Jolly Rancher! That's quite a prize, eh? (I'll also post a clue to every slice today, so keep checking.)

Here's the riddle: There are 25 in my slice; one is missing. Which is it?

And as the slices came in, I provided the following clues:

It’s not you.

It’s not why.

Are is not it.

Gee, no.

It’s not, eh?

It’s not the eye.

Oh? No.

N NO

See? No.

K NOT

Tease there

So’s z

Andy

4Fs

Mmmmmmmmmm

It’s naughty.

J’s in jolly.

So many els

X? Present!

What about you, dear reader? Can you solve the riddle?