Does temperature increase during melting?
Depends on the purity.
In pure substances, temperature is constant during melting.
In mixtures, temperature increases during melting.
A pure substance (for example iron) will have a constant temperature during the melting process, since the heat given is used to melt the substance (latent heat).
However, if the solid is a mixture of substances, their melting points are different. Once the lower melting point is reached, that substance starts to melt, but the other substances still do not melt, which means the heat is not used as latent heat, so the temperature rises.
Note : Same applies to gases.