Which characteristic is true of intermetallic compounds?

Intermetallic compounds are characterized by their distinct properties that arise from the bonding between different metallic elements. The correct choice highlights that these compounds are typically hard and brittle, which is a key feature. This brittleness occurs because intermetallics often have ordered structures that do not allow for easy dislocation movement, making them less ductile than many pure metals.

Additionally, intermetallic compounds usually possess higher melting points compared to their constituent elements. This can be attributed to the strong bonding interactions present in the ordered structures of these compounds. Higher melting points are a common characteristic of many intermetallic compounds, reflecting the stability and strength of the bonds formed between the elements.

In contrast, the other provided options describe characteristics that do not align with the typical behavior of intermetallic compounds. They are generally not flexible or ductile; in fact, these compounds are often used in applications where hardness is required, but their brittleness limits their use in situations where deformation might occur. Similarly, intermetallic compounds do not have lower melting points than the constituent elements and are not found in a liquid state under normal conditions, as they typically exist in a solid form.