Answer
$\color{red}{\text{This expression is a polynomial}}$.
Work Step by Step
Remember that a term is considered as a monomial ONLY IF it is a PRODUCT of constants and/or variables.
In this item, the terms are $\dfrac{1}{4}x^{10}$ and $-8.6$ and each can be considered as a monomial. Therefore, $\color{red}{\text{this expression is a polynomial}}$.