Which one of the following ia a characteristic of a metal?

Assuming your options are changes the color of litmus paper to red, conducts heat readily, reacts with bases to produce salts, and b ecomes negative when combined with other elements, the correct answer is conducts heat readily.

This is because the electrons in the metal are allowed to float the space freely, and they are not stuck together like in some solids - this is the reason why they can carry kinetic energy throughout the metal, which is of course related to heat as well. The other options do not refer to metals at all.