The given bar graph represents the pass percentage of 10th and 12th classes of a school during the consecutive four year period 2016-2019.

What is the average of percentage of the failed students of the 12th class for all four years?

From the bar graph,

Percentage of failed students of 12th class in 2016 = 100 - 71 = 29%

Percentage of failed students of 12th class in 2017 = 100 - 82 = 18%

Percentage of failed students of 12th class in 2018 = 100 - 66 = 34%

Percentage of failed students of 12th class in 2019 = 100 - 84 = 16%

$$\therefore\ $$Average of percentage of the failed students of the 12th class for all four years = $$\frac{29+18+34+14}{4}=\frac{95}{4}=23.75\%$$

Hence, the correct answer is Option D