Question

Which sentence is correct?



Each guitar must be in his or her own case.


Each guitar must be in their own case.


Each guitar must be in its own case.

Answer 1

"Each guitar must be in its own case." is the best choice.

Reason: "Each" is singular, so it needs a singular pronoun; guitars are inanimate, so the neuter singular "its" is appropriate.
Notes: "his or her" is awkward because guitars are not people; singular "they/their" is increasingly used for people but is less natural for inanimate nouns — you could rephrase as "All guitars must be in their own cases" if you prefer plural wording.