"Nine pupils" is correct.
Pupils'. When you have a plural possessive, then the apostrophe goes after the s. If a pupil owns something, that is the pupil's stuff. If pupils collectively own something, that is the pupils' stuff.
"Pupil's" is the possessive form of "pupil," indicating that something belongs to or is associated with a single pupil. "Pupils'" is the plural possessive form of "pupil," indicating that something belongs to or is associated with multiple pupils.
The plural form for the noun pupil is pupils.The plural possessive form is pupils'.Example: Some of our pupils' essays were published in the school newsletter.
pupil slipups, pupils slipup, pupils pupils, slipup pupils
Pupil
There should be an apostrophe in that phrase. If you're referring to one pupil, it's "pupil's classroom." If you're referring to a group, it's "pupils' classroom."
The plural form for the noun pupil is pupils.The plural possessive form is pupils'.Example: Some of our pupils' essays were published in the school newsletter.
Sheep and goats have horizontal, oval pupils.
The phrase that means that someone's pupils contract when a bright light is shone into their eyes is "pupils reactive" ... they react to the light. If they don't react to the light, they'd be described as "pupils fixed and dilated."
As always the use of an apostrophe is determined by the meaning you want to give the word.Pupils: more than one pupil e.g. There are 30 pupils in this class. (There is more than one)Pupil's: owned by a pupil e.g. Have you seen this pupil's book? (The book that belongs to the pupil)Pupils': owned by more than one pupil e.g. I want to talk to you about the pupils' behaviour. (the behaviour 'belonging to' more than one pupil)NB Pupil can mean two things. A pupil can be a student at a school, which is how the word is used in the above examples.'Pupil' is also the name of the transparent portion of the eye (the black dot in the middle). They are treated the same grammatically, but the example sentences would be different.
We are pupils and we are flying in a roflcopter
pupil pupils