Final answer:
When cooling 3.5 kg of austenite containing 0.95 wt% C to below 727 °C, ferrite is formed.
Step-by-step explanation:
To determine the phase change when cooling 3.5 kg of austenite containing 0.95 wt% C to below 727 °C, we need to consider the phase diagram for the iron-carbon system. At below 727 °C, ferrite is formed, which is a solid solution of carbon in iron. This phase change occurs because the carbon concentration is below the eutectoid composition of 0.77 wt% C, where pearlite would be formed.
Therefore, the answer is a) Ferrite is formed.