The correct option is C 81mn, 96m2n2
Literal Factor:––––––––––––––––––
Literal factor is a part of an algebraic term without the constant.
For example, 2x2y–––––– and 5y––– have literal factors as x2y–––– and y–– respectively.
Now, let's take a look at each pair of terms one-by-one.
∙ (a.) 10pq, 20pq:–––––––––––––
Both the terms have the same literal factor as pq–––.
∙ (b.) 256ab, 562ba:––––––––––––––––
Both the terms have the same literal factor as ab–––.
(∵ab=ba; Multiplication is commutative)
∙ (c.) 81mn, 96m2n2:––––––––––––––––––
Both the terms have different literal factors. 81mn–––––– has literal factor as mn–––– and 96m2n2–––––––– has literal factor as m2n2––––––.
∙ (d.) 786rs, 144rs:––––––––––––––––
Both the terms have the same literal factor as rs–––.
Therefore, option (c.) is the correct answer.