The mode of the following data is 36. What is the value of x ?

As per given data, 

Class interval of 30-40 has highest frequency, thatswhy it is modal class

As we know, 

M = $$l+\left\{\frac{\left(f_1-f_0\right)}{2f_1-f_0-f_2}\right\}\times\ h$$

where, h= size of the class interval, 

l = lower limit of the modal class, 

$$f_{1=}$$ frequency of the modal class, 

$$f_{_0=}$$ frequency of the class preceding the modal class

$$f_{_2=}$$ frequency of the class succeeding the modal class

putting the values from the given data : 

$$36=30+\frac{\left(16-10\right)}{2\times\ 16-10-x}\times\ 10$$

$$36-30=\frac{6}{22-x}\times\ \ 10$$

$$22-x=10$$

$$x=12$$

Hence, Option D is correct.