Final answer:
The degree of the expression -5a⁴ is 4 because the highest power of the variable, a, is 4. The name of the expression is quartic because it is of degree 4.The expression -5a⁴ has a degree of 4, hence it is called a quartic polynomial.
Step-by-step explanation:
The expression -5a⁴ has a degree of 4 since the highest exponent of the variable 'a' is 4. The name corresponding to a polynomial with one term with a degree of 4 is a quartic. Therefore, the correct answer is that the degree of the expression is 4, and the name using the number of terms for the expression is quartic.