Which account balance in a trial balance is likely to indicate an error?

The correct answer highlights an important principle in accounting related to the typical nature of account balances. Accumulated Depreciation is a contra asset account, which means it is used to offset the value of a related asset to reflect a more accurate net book value. This account typically carries a credit balance, representing the total depreciation expense that has been recognized for the asset over time.

If Accumulated Depreciation shows a debit balance, this indicates an inconsistency, as it suggests that the account has been incorrectly recorded or managed. An unanticipated debit balance could imply that more depreciation has been reversed than recorded, which would be a significant error in accounting.

In contrast, the other options depict scenarios that are consistent with standard accounting practices: Inventory typically holds a debit balance as an asset; Discount on Bonds Payable normally has a debit balance reflecting reductions in interest costs; and Allowance for Doubtful Accounts, being a contra asset account, usually has a credit balance to represent anticipated uncollectible accounts. Thus, the debit balance in Accumulated Depreciation stands out as an anomaly and indicates a likely error in the financial records.