The given Bar Graph presents the number of students of two schools for six years.

In which year, the percentage increase of students in school A is the highest in comparison to its previous year?

There is a decrease in number of students in school A in 2010 compared to its previous year

Percentage increase in number of students in school A in 2009 compared to its previous year$$\ =\frac{\left(800-640\right)\ }{640}\times100=25$$

Percentage increase in number of students in school A in 2011 compared to its previous year$$\ =\frac{\left(700-500\right)\ }{500}\times100=40$$

Percentage increase in number of students in school A in 2012 compared to its previous year$$\ =\frac{\left(900-700\right)\ }{700}\times100=28.5$$

Hence, the correct answer is Option C