Answer: Thermal conductivity of wire
Step-by-step explanation:
The hypothesis of the experiment is to find the thermal conductivity of the the wires. The independent variable in the experiment is the type of wire used.
There are two types of wire used in the experiment one is copper and other one is steel. Rest all the variables are control variable.
At the end of the experiment the thermal conductivity was determined. This is the dependent variable of the experiment.
Hence, the correct answer is option D