In which type of chemical reaction do two or more substances combine to form one substance?

Explanation:

A reaction in which two or more substances combine together to form a single product is known as synthesis reaction.

For example,

     or,        

During synthesis reaction, heat or light are released in the form of energy. Therefore, synthesis reactions are exothermic in nature.

metals are good conductor of electricity. it has free electrons on their surface. according to electron pool theory, each atom present in a metal crystal losses all of its valence electron and as a result a pool of free is form. these pool of electrons are free to move and   conduct electricity easily   while making metal as good conductor.

the correct answer is a. the ability of electrons to flow throughout the metal.

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