2) The mass after the reaction will also be 30 grams.
3) The mass of the product will be 149 grams.
Law of conservation of mass
The law of conservation of mass states that mass can neither be created nor destroyed during the course of a reaction. However, the mass can be converted to different forms during the course of the reaction.
Thus, if 30 grams of elements react, the mass after the reaction will remain 30 grams. Although the elements might have been converted to different forms.
If potassium reacts with chlorine to produce potassium chloride, the equation of the reaction will be:
 K + Cl ---> KCl
78 g of potassium = 78/39 = 2 moles
72 g of chlorine = 71/35.5 = 2 moles
2 moles of KCl = 2 x 74.5 = 149 grams.
More on the law of conservation of mass can be found here: https://brainly.com/question/13383562
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