Which characteristic is not associated with alkali metals?

Alkali metals, which include elements like lithium, sodium, potassium, and others, are known for their distinct properties. One key characteristic is their excellent conductivity of electricity. This is due to their atomic structure, which allows them to easily lose one electron, creating a free-moving charge that facilitates conductivity. As a result, alkali metals are generally very good conductors of electricity.

In contrast, the other options accurately reflect the properties of alkali metals. They react vigorously with water, forming hydroxides and releasing hydrogen gas—showing their high reactivity. Their softness and low density make them easy to cut with a knife, and they have a shiny, metallic luster when freshly cut. Therefore, being poor conductors of electricity is not a characteristic associated with alkali metals, making this the correct choice.