Will a single pole 20 amp breaker be OK for refrigerator and microhood? If so, I have to switch the current 30 amp double pole breaker with 2 black wires for the new 20 amp single pole. Does the extra black wire go to the bus bar?

Whoa! It's not that simple.

What is this existing circuit feeding? How many wires?

And no, a single 20A circuit is not OK for both a refer and micro/hood. Normally the micro/hood requires it's own dedicated circuit.

Whoa! It's not that simple.

What is this existing circuit feeding? How many wires?

And no, a single 20A circuit is not OK for both a refer and micro/hood. Normally the micro/hood requires it's own dedicated circuit.

Sorry, I had asked previously about this circuit. The previous owners used this circuit for multiple receptacles. I have made a junction box with 12/2 going out to the 2 receptacles I was hoping to use for the microhood & ref. One of the answers I received previously was to switch out the 30 amp with a 20 amp. Is this not correct?

I agree with Stan, as many microwaves consume a 20 ampere circuit by themselves...
I've always thought it was worth the effort (and cost) to provide a dedicated circuit to my refrigerator. If you have ever seen (or smelled) a frig full of food without power for a few days, I think you'd agree that it would be worth protecting...