The correct option is Remove-Mailbox.

Remove-Mailbox is the Exchange Online PowerShell cmdlet that removes an Exchange mailbox object. You run this cmdlet against Exchange Online with the Exchange Online PowerShell module and an account that has the required administrative role in order to delete or disable a mailbox in the tenant.

Remove-TeamUser is incorrect because that cmdlet removes a user from a Microsoft Teams team and it does not affect Exchange or mailboxes.

Remove-MailboxPermission is incorrect because that cmdlet changes or removes access rights such as FullAccess or SendAs on a mailbox and it does not delete the mailbox itself.

Remove-MsolUser is incorrect because that cmdlet comes from the MSOnline module and is used to remove an Azure Active Directory user account. It is not the Exchange cmdlet for mailbox removal and the MSOnline module is deprecated so it is less likely to be the focus of newer exams.

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