Final answer:
In accounting, closing entries transfer temporary account balances to a permanent owner's equity account. Option 3, Salaries Payable to Income Summary, is not a closing entry because it involves a liability account.
Step-by-step explanation:
The student is asking about closing entries in accounting. The correct answer to the question, 'Which of the following is NOT a closing entry?' is option 3: Salaries Payable 100; Income Summary 100. Closing entries are used at the end of an accounting period to transfer the balances of temporary accounts to a permanent owner's equity account.
Closing entries typically involve revenue and expense accounts and the Owner's Withdrawals account. They do not involve liability accounts such as Salaries Payable, which makes option 3 incorrect as it represents a recording of owed salaries, not a closure of a period's transactions.