1. **State the problem:** Determine which expression is a monomial upon simplification between $\frac{x^4}{x^5}$ and $\frac{x^3}{x^2}$. A monomial is a polynomial with only one term and variables with non-negative integer exponents. 2. **Recall the rule for dividing powers with the same base:** $$\frac{x^a}{x^b} = x^{a-b}$$ 3. **Simplify the first expression:** $$\frac{x^4}{x^5} = x^{4-5} = x^{-1}$$ 4. **Interpret the result:** The exponent is $-1$, which is a negative integer. Polynomials cannot have negative exponents, so this is not a monomial. 5. **Simplify the second expression:** $$\frac{x^3}{x^2} = x^{3-2} = x^{1} = x$$ 6. **Interpret the result:** The exponent is $1$, a positive integer, so this is a monomial. **Final answer:** The expression $\frac{x^3}{x^2}$ simplifies to $x$, which is a monomial. The expression $\frac{x^4}{x^5}$ simplifies to $x^{-1}$, which is not a monomial.