"Unearned revenue" is what type of account? 1. asset 2. liability 3. owner's equity 4. income?

It is that income which is received but not yet earned, In other words you got paid for a service that you have not yet provided or got paid for goods that are not yet sold.
So it comes under CURRENT LIABILITIES .You ll make the Entry by (debit-cash) (Credit-Unearned income) and when you have earned it, you ll make the entry (Debit-unearned income) (credit-Income)

Unearned revenue is the amount received for those product or services which product or service still not received by customer, therefore it is liability untill service or goods not deliver to customer.

Unearned revenue is a liability.
It is revenue received but not earned yet.
An example is rental income received in advance.
Unearned revenue is recorded as a debit to Cash account and credit to Unearned Revenue account.

LIABILITY

Payment received before a good is sold or a service is provided.
Unearned revenue is classified as a current liability on the balance sheet until it is recognized as earned during the accounting cycle.

2) Liability When an individual or company receives money for a service or product that has yet to be fulfilled.
Unearned revenue can be thought of as a "pre-payment" for goods or services which a person or company is expected to produce to the purchaser.
As a result of this prepayment, the seller now has a liability equal to the revenue earned until deliver of the good or service.

LIABILITY SINCE INCOME IS NOT EARNED YET.

Option -2 , Liability: Unearned revenue is advance received for future sale of goods or services.

2.Liability

Unearned Revenue is the advance payment made by the customer for  service or goods to be provided in near future. so unearned revenue is a current liability.

unearned revenue on the other hand called Accrued income.
I have responded for accrued income in one of the revenue recongnistion question.
for example we have a Fixed deposit or any other financial instrument which carries either fixed or variable % of earnings for a period.
When we close our books these income is not actually given by the instrument provider.
but we can book these as an income on a pro-rata basis into the books for the period falling within our accounting period.
Though we havent received the benefit on hand still we can book it as income.
Because these income will come on a date when the instrument is maturing but all income is not of the future period something belongs to the current period.
this is the unearned revenue and can be treated as Other current assets.