Which of the following is not a property of a transition metal? 

They have low boiling points

The correct answer is option 4. They have low boiling points.

Transition metals are characterized by several properties, including being lustrous (having a shiny appearance), malleable (capable of being hammered or rolled into thin sheets), and ductile (capable of being drawn into thin wires). However, one of the distinguishing features of transition metals is that they generally have high melting and boiling points compared to the main group elements. Therefore, the statement "They have low boiling points" is not a property of transition metals.