Odd One Out:
Provision for discount on debtors A/C
Provision for doubtful debts A/C, Reserve for discount creditors A/C, and Provision for depreciation A/C are all related to accounting for expected losses or expenses. However, Provision for discount on debtors A/C stands out as it is related to expected discounts on sales to debtors, rather than expected losses or expenses.

Explanation:

Provision for doubtful debts A/C:
- This account is created to account for potential losses due to customers defaulting on their payments.
- It is a common practice in accounting to set aside a certain amount as a provision for doubtful debts to ensure that financial statements reflect a more accurate picture of the company's financial position.

Reserve for discount creditors A/C:
- This account is created to account for expected discounts that the company will have to give to its creditors.
- It is important to accurately record these discounts in order to reflect the true cost of goods sold and maintain proper accounting practices.

Provision for depreciation A/C:
- This account is created to account for the depreciation of fixed assets over their useful life.
- By setting aside a certain amount as a provision for depreciation, companies can spread out the cost of the asset over its useful life and accurately reflect the value of the asset on the balance sheet.

Provision for discount on debtors A/C:
- This account is created to account for expected discounts that the company will have to give to its debtors.
- Unlike the other accounts mentioned, this account is related to discounts given to debtors rather than expected losses or expenses, making it the odd one out in this context.