What is the equivalent resistance for a series circuit with three resistors: 5.0 ohms, 2.0 ohms, and 12.0 ohms?

a. 19 ohms
b. 6.3 ohms
c. 2.0 ohms
d. 120 ohms

There are several information's already given in the question. Based on those given information's, the answer can be easily deduced.
Equivalent resistance = 5 + 2 + 12
                                   = 19 ohms

From the above deduction, it can be deduced that the correct option among all the options that are given in the question is the first option or option "A". I hope that this is the answer that has actually come to your desired help.

Answer sample (c); // would be best because the percentage of the energy in an incident wave that remains in a reflected wave from this material is the smallest;