What is the total mass in grams of 0.013 mole of #I_2#?
The key here is the molar mass of iodine, which is listed as
#M_ ("M I"_2) = "253.81 g mol"^(-1)#
The thing to remember about the molar mass of a chemical substance is that you can use it as a conversion factor to go from moles to grams or vice versa.
In other words, the molar mass allows you to figure out how many grams are needed in order to have exactly
In this case, you need
This means that
#0.013 color(red)(cancel(color(black)("moles I"_2))) * overbrace("253.81 g"/(1color(red)(cancel(color(black)("mole I"_2)))))^(color(blue)("the molar mass of I"_2)) = color(darkgreen)(ul(color(black)("3.3 g")))#
The answer is rounded to two sig figs, the number of sig figs you have for the number of moles of iodine.