Answer
Not a monomial (because there are variables in the denominator)
Work Step by Step
A monomial is an expression of the form $ax^{k}$,
where $x$ is the variable,
the exponent $k$, a nonnegative integer, is the degree,
and $a$ is the coefficient of the term.
The given expression is a quotient of a monomial $(-2x^{2})$ and a binomial $(x^{3}+1)$.
Thus, it is not a monomial because there are variables in the denominator.
