The molar mass of #NO_2# is 46.01 g/mol. How many moles of #NO_2# are present in 114.95 g?
A substance's molar mass tells you the mass of one mole of that substance.
In your case, nitrogen dioxide,
So, in essence, molar mass is simply a conversion factor between number of molecules and mass.
Since you need
#114.95 color(red)(cancel(color(black)("g"))) * "1 mole NO"_2/(46.01color(red)(cancel(color(black)("g")))) = "2.49837 moles NO"_2#
Rounded to four sig figs, the number of sig figs you have for the molar mass of the compound, the answer will be
#n_(NO_2) = color(green)("2.498 moles")#