(14.007 g/mol + 3.02 g/mol)(8.60791 mol)

Significant Figure Rules: 
For Addition/Subtraction you round to the last place value you have in common. In the case of:
14.007 g/mol + 3.02 g/mol 

It is the Hundreth spot.
So... your answer to that part of the problem would come out as: 
17.027 g/mol, but you need to round it to the nearest hundreth. 
So, 17.03 g/mol is the correct amount. 

(17.03 g/mol)(8.60791 mol)

For multiplication you follow the significant figure rules. In this case 17.03 g/mol has the least amount of significant figures (4) so we'll round to that many. 

146.6 g is the answer!

Note that the answer, 146.6g, has lost the moles, because we canceled them out. (It came out to be 146.6 g*mol/mol, and when something is it over itself it cancels out!) 

Hello thereone of the following properties was originally used to arrange elements on the periodic table, but is no longer used to organize the modern version. which property fits this description? answer: atomic mass  was originally used to arrange elements on the periodic table, but is no longer used to organize the modern version.