CBSE Class 10 Answered

A metal has large number of free electrons and due to this they conduct current and heat.The resistivity if a material or conductor is the hindrance or resistance offered by its structure to the free electrons to flow.

Generally pure metals have low resistivity as they have large number of free electrons and low hindrance due simple atomic arrangement but when two or more metals are combined then the atomic arrangement changes and this changes the number of free electrons as well as increases the hindrance to their flow. Thus alloys have higher resistivity then its constituent metals.