If the cost price of $10$ shirts is equal to the selling price of $8$ shirts, then which of the following is true for the transaction?

The correct option is C. Profit of $25\%$
Let the cost price of $1$ shirt is Rs.$1$
So, the cost price of $10$ shirts is Rs.$10$
As per problem, C.P. of $10$ shirts = S. P. of $8$ shirts
S.P. of $8$ shirts = Rs. $10$
S.P. of $1$ shirt = Rs. $\frac{10}{8}$ = Rs. $\frac{5}{4}$
So, profit = S.P – C.P
= Rs. $\left(\frac{5}{4}\right)$ – Rs.(1)
= Rs. $\frac{1}{4}$
Profit $\%$ = $\left\{\left(\frac{1}{4}\right)\right\}$ $\times$ $100\%$
$=25\%$.