If the cost price of 18 articles is equal to the selling price of 16 articles, the gain or loss is = ?

Answer: Option D

According to the question,
18 Cost Price = 16 Selling Price
$$\begin{array}{rl}& \frac{\text{CP}}{\text{SP}}=\frac{16}{18}=\frac{8}{9}\}\text{1 unit profit}\\ & \text{Profit}\%=\frac{1}{8}\times 100\\ & =12\frac{1}{2}\%\text{ gain}\end{array}$$