Answer:
Dr Available for sale securities 11,500
Cr Unrealized gains - AFS securities 11,500
Explanation:
The securities cost is $420,000 while the fair market value is $431,500, so the difference is an unrealized gain of = $431,500 - $420,000 = $11,500.
Unrealized gains are included in Other comprehensive income account, which belongs under stockholder equity. When unrealized gains increase, then they should be credited.
Since the securities are held as investment assets, they should also increase by debiting the account.