Explanation:

- Option 1: Bills Receivable

- Bills receivable are promises to receive payment in the future. They are considered liquid if they are short-term and easily convertible to cash.

- Option 2: Debtors

- Debtors represent amounts owed by customers. They are liquid if the collection period is relatively short and predictable.

- Option 3: Inventory

- Inventory includes raw materials, work-in-progress, and finished goods. It is generally not considered liquid because it needs to be sold before it turns into cash.

- Option 4: Bank Balance

- Bank balances are the most liquid asset as they are already in cash form.

Option 3: Inventory is the correct answer.