Answer:
Dr unrealized holding gains and losses—OCI  $20,000
Cr investment in bonds fair value adjustment        $20,000
Dr investment in bonds fair value adjustment        $30,000
Cr unrealized holding gains and losses—OCI                 $30,000
Explanation:
On 31st December 2021 the adjustment required is the difference between the cost of bond investment of $600,000 and the market value of the bonds which was $580,000, in a nutshell a unrealized loss of $20,000 is recorded.
The excess of fair value of market value of $610,000 over the previous year market value would be debited to fair value adjustment while it is also credited to unrealized holding gains and losses-OCI