If an article sold at 200% profit then the ratio of its cost price to his selling price will be = ?

Answer: Option C

Let the cost price of the article is = Rs. 100
According to the question,
$$\text{100 (cp)}\stackrel{200\%\text{ profit}}{\to }\text{300 (sp)}$$
$$\text{Ratio of }\frac{\text{CP}}{\text{SP}}=\frac{100}{300}=\frac{1}{3}$$