I'm really having trouble with this science worksheet, it's about reactants and products

Water ionizes by the equation h2o(l)⇌h+(aq)+oh−(aq) the extent of the reaction is small in pure water and dilute aqueous solutions. this reaction creates the following relationship between [h+] and [oh−]: kw=[h+][oh−] keep in mind that, like all equilibrium constants, the value of kw changes with temperature.

Zoe is investigating the composition of substance a, an unknown substance. using chemical processes, she analyzes substance a and determines it is composed of sodium, oxygen, and hydrogen atoms in a ratio of 1 : 1 : 1. what is substance a? a. a compound b. an element c. a heterogeneous mixture d. a homogeneous mixture

According to each substances heat of fusion, which of the items below requires more heat to be added per gram of substance to go from solid to liquid? silver sulfur water lead