Which sample has the greatest number of atoms in it?

Question

A. 2 g of Hydrogen
B. 7 g of Lithium
C. 8 g of Helium
D. 110 g of Silver
E. 200 g of Gold

Answer 1

One mol will always contain avogadro's number of atoms. Thus, this will basically be equal to whichever option has the most mol which you find by dividing each mass by the element's molar mass:

 

2g H / (1.008 g/mol H) = 1.98 mol H

 

7g Li / (6.941 g/mol Li) = 1.01 mol Li

 

8g He / (4.003 g/mol He) = 2.00 mol He

 

110g Ag / (107.868 g/mol Ag) = 1.02 mol Ag

 

200g Au / (196.967 g/mol Au) = 1.02 mol Au

 

Helium has the most number of mol out of all the options and will thus have the highest number of atoms. 

Answer 2

Look up the atomic weight (in grams per mole) of each of these 5 elements, and divide the given mass of the element by its atomic weight.  That gives the number of moles of each element.  The one that gives the greatest number of moles has the greatest number of atoms.