Which material does not melt at any temperature? wood, a mixture of different substances ethanol, a molecular compound sodium chloride, an ionic compound iron, a metallic element description?

The material, which does not melt at any temperature is WOOD.
Wood is made up of many substances including lignin, water, cellulose and other organic materials. When wood is heated, it normally oxidizes in the presence of oxygen before it has the chance to melt. The physical structure of the wood is typically destroyed during this process and the original material can not be obtain again.This irreversible breakdown of wood makes it impossible for wood to melt. 

A. volume stays constant. just took took the quiz

Ibelieve it is b. proton.hope my answer has you : )