Why does increasing the temperature cause a solid substance to change in succession from a solid to a liquid to a gas?

Increasing temperatures cause the molecule in the substance to gain kinetic energy and begin to vibrate and move at high momentum. This allows the molecules in the substance to break from the bonds of the lattice in the solid hence melt to a liquid. More heating gives the molecules more kinetic energy and enables the molecule to further move away from each other and transform to gas.

a compound is a molecule made of atoms from different elements.

a. by the combination of an unlimited number of elements

answer:

technetium is the most reactive. this is followed by silver. the least reactive out of these three elements is strontium.