Sally here received the cash for the services to be performed in July. Thus, she has received cash for the unearned revenue.
The journal entry to record the cash received for unearned revenue is -
Cash Dr... XXX
Unearned revenue Cr. XXX
Thus, the correct entry here will be -
Cash Dr. $ 500
Unearned Revenue Cr. $ 500
The correct option is a. Cash $ 500 Unearned revenue $ 500.