Iron is ferromagnetic:
A. at all temperatures
B. at NTP only
C. above 770°C
D. below 770°C

Iron is a ferromagnetic material below 770°C.
Explanation:
• Ferromagnetic materials, like iron, exhibit strong magnetic properties because of the alignment of their magnetic domains.
• At temperatures below 770°C (also called the Curie temperature), iron remains ferromagnetic.
• Above 770°C, iron undergoes a phase transition to a paramagnetic state, where the alignment of magnetic domains is lost, and it no longer exhibits ferromagnetic properties.
Therefore, the correct answer is: D) Below 770°C.