3.4 X 10^-2 because you start your equation with 2.5g in your (what we call train tracks). Then you have to find the GFM (gram formula mass) of KCl (potassium chloride). You find this by adding the average atomic mass of each element. Potassium's is 39.10 and Chlorine's is 35.45 which gives you a total of 74.55 grams per mol. so now that you have found the GFM you plug that number into the diagonal bottom in order to cancel the gram units. Then you would place 1 mol KCl on top because that is the unit you want. Finally you will divide your original 2.5 by the GFM of 74.55 to get an answer of 0.033534 mol KCl... but since sig figs matter your final answer will be 3.4 X 10^-2
The octet rule refers to the tendency of atoms to prefer to have eight electrons in the valence shell. When atoms have fewer than eight electrons, they tend to react and form more stable compounds
