The higher melting point of sodium fluoride compared to sodium iodide is due to stronger forces of attraction between the ions in the crystal lattice of the fluoride compound. Fluoride ions are smaller and have a higher charge density compared to iodide ions, leading to stronger electrostatic forces between the ions in sodium fluoride, resulting in a higher melting point.
The residue from the reaction between ferric chloride and sodium hydroxide would likely contain iron hydroxide as a major component, with sodium chloride also present because of the initial reactants. The specific composition would depend on the stoichiometry of the reaction and any other impurities present in the starting materials.
NaCl is neutral because sodium has a valency of +1 and chlorine has a valency of -1, meaning that when they form a bond the solution is neither positive or negative. Hence, 1 -1 = 0 In addition, NaCl is known as a neutralization solution and it is assumed by many as being a neutral solution.