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There are 5 significant figures in the following number. All of the numbers essentially are significant.
Explanation
Radius of neon atom : 69 pm = 
Volume occupied by the one atom:

given that
atoms are present in 1L
1 L = 0.001 
The volume occupied by the
neon atoms

Fraction of volume occupied by the neon atom:


The fraction of of volume occupied by the neon atom is very less than the 1 L which indicates the presence of large amount of empty space between the atoms of the gas.
First, find out how many grams are in one mole of CO2(the two oxygen atoms means you need to multiply oxygen’s amu by 2,then add whatever carbon’s amu is to that). Then divide 26 grams by that number and that will be your moles. There are only two significant figures, so round your answer correctly.
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