You have 10.0 g each of na, c, pb, cu and ne. which contains the smallest number of moles?

Number of moles of an element present can be calculated by dividing the mass present by the molar mass
the mass present is 10.0 g of each of the following elements
               
                                 Na               C                Pb                  Cu        Ne
molar mass             23 g/mol  12 g/mol   207.2 g/mol   63.5 g/mol    20.17 g/mol
number of moles     = 0.43       =0.83          = 0.048          = 0.157   = 0.4958
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from the calculated number of moles, Pb contains the smallest number of moles.
since mass present is constant for all the elements, the number of moles was inversely proportional to molar mass, therefore Pb has the highest molar mass hence the least number of moles

Matter- occupies space and possesses rest massno matter is the opposite