What is a key characteristic of molten iron collected in the blast furnace?

Molten iron collected in the blast furnace is characterized by its great strength. This strength is a crucial property of iron that makes it suitable for various structural applications. When iron is extracted from its ore in the blast furnace, it is subjected to high temperatures and combines with carbon, which enhances its strength and other mechanical properties.

While the other options may refer to aspects of iron in different contexts, they do not accurately describe molten iron from a blast furnace. For instance, molten iron is not lightweight; it is dense and heavy. Additionally, it is actually a good conductor of electricity, contrary to the statement about conductivity. Finally, the iron produced is not pure; it contains various impurities, including carbon, which are typically present in the molten state. Thus, the key characteristic of strength is what makes molten iron particularly important in construction and manufacturing processes.