I think the correct answer from the choices listed above is option B. The reactants calcium sulfide and sodium sulfate will react and form a precipitate which is calcium sulfate since it is only slightly soluble in aqueous solution. Hope this answers the question.
NO₂ is a brown gas while N₂O₄ is colorless. If heating causes a brown color to persist, then this means that heating causes the reaction to shift backwards and produce NO₂. Therefore, the reaction must be exothermic.
To calculate electronegativity, start by going online to find an electronegativity table. You can then assess the quality of a bond between 2 atoms by looking up their electronegativities on the table and subtracting the smaller one from the larger one. If the difference is less than 0.5, the bond is nonpolar covalent.
