Final answer:
The question inquires about the volume change when iron undergoes allotropic transformation from BCC at 912°C. However, without information on the final structure and its packing efficiency, the percent volume change cannot be calculated.
Step-by-step explanation:
The question asks about the allotropic transformation of iron at 912°C. Allotropic transformation refers to a change in the crystal structure of an element while it remains in the same physical state.
In the case of iron, it transforms from a body-centered cubic (BCC) structure to a face-centered cubic (FCC) or other structures at higher temperatures. The BCC structure for iron, which is stable below 910°C, has atoms efficiently packed, occupying about 68% of the total volume.
Calculating the percent volume change would require information about the final structure and its packing efficiency. Since this information is not provided in the question, a precise answer can't be determined without additional data.