What has to do with the closeness of a measurement to the true value?

Which substances have the lowest melting points: ionic covalent, or metallic

What is the ph of a solution that has a hydrogen ion concentration of 1.0 * 10 -9 m?

The chemical equation below shows the reaction of sodium (na) and chlorine (cl) to form sodium chloride (nacl). 2na + cl2 → 2nacl in this equation, which of the following is a reactant? i. sodium ii. chlorine iii. sodium chloride