If I would have purchased 11 articles for Rs. 10 and sold all the articles at the rate of 10 for Rs. 11, the profit percent would have been = ?

Answer: Option C

Cost price of 11 oranges = Rs. 10
Cost price of 1 orange = Rs. $$\frac{10}{11}$$
Selling price of 10 oranges = Rs. 11
Selling price of 1 orange = Rs. $$\frac{11}{10}$$
Since Selling price > Cost price, there is profit
Profit per orange = Selling price - Cost price
$$\begin{array}{rl}& =\text{Rs}\text{.}\frac{11}{10}-\text{Rs}\text{.}\frac{10}{11}\\ & =\text{Rs}\text{.}\frac{121-100}{110}\\ & =\text{Rs}\text{.}\frac{21}{110}\end{array}$$
Profit on 11 oranges $$=\frac{21}{110}\times 11=\text{Rs}\text{.}2.1$$
$$\begin{array}{rl}& \text{Profit}\%=\frac{\text{Profit}}{\text{Cost}\text{Price}}\times 100\%\\ & =\frac{2.1}{10}\times 100\%\\ & =21\%\end{array}$$