Answer:Debit
Explanation:
Stock account is a capital account and in credit balance.
The purchase of 50 shares of $10 value for $20 will result in a $500 loss and the sales of 10 shares at $25 gives a gain of $50 which reduce the total loss to $450.
Since the treasury stock accounts is a credit balance the loss will be debited to it to reduce the value of treasury stock