Letter D is the correct answer.
So, an 8-year-old child who scores like an average 10-year-old on an intelligence test would have a mental age of 10 and an IQ of 125.
The answer for this question is quite simple if we use the IQ formula:
(Mental Age / Chronological Age) x 100 =
In this case, we would have:
( 10 / 8 ) x 100 =
1.25 x 100 = 125.