The intelligence quotient was devised by Stern and popularised by Terman as a single number that compares a child's tested ability with the ability typical of that chronological age. It is obtained by dividing the age indicated by the test performance by the actual age and multiplying the result by one hundred.

Because the numerator of that ratio is the age level a child reaches on reasoning, memory, vocabulary, number and problem solving tasks, the figure reports how far the thinking side of the child has advanced in relation to peers. A quotient near one hundred means the child reasons about as well as most children of the same age.

The other choices are measured in quite different ways. Height, weight and motor skill are read from physical measurements; traits, attitudes and adjustment come from personality inventories and observation; the control and expression of feelings is assessed separately. None of these is what the quotient reports.

Mental option is correct.