-  Let a% of 25 = 2.125. Then , (a/100) x 25 = 2.125 a = (2.125 x 4) = 8.5

To find the missing figure in the given equation, we need to use the concept of percentages and solve for the unknown percentage.

We are given that "?% of 25 = 2.125". This means that some percentage of 25 is equal to 2.125. We can write this as an equation:

(?/100) x 25 = 2.125

To solve for the unknown percentage, we can isolate the variable "?". First, we simplify the left-hand side by multiplying 25 and "?/100". This gives:

(25 ?)/100 = 2.125

We can further simplify this equation by multiplying both sides by 100, which gives:

25 ? = 212.5

Finally, we can solve for "?" by dividing both sides by 25, which gives:

? = 8.5

Therefore, the missing figure in the given equation is 8.5.

Hence, the correct answer is option B.