Answer:
2352.15g or 2.4kg (significant digits)
Step-by-step explanation:
Assuming that it's 5.4*10^24 molecules of Ba(NO3)2, We know that a mole has 6.02* 10^23 molecules. Dividing the given number by Avagadro's number, we can determine how many mols are there.
(5.4*10^24)/(6.02*10^23)=8.970099668...
lets round this to 9.0 moles (Significant Digits.)
now knowing this, we can take the atomic mass of the compound(I measure using my school's given masses, may be different for you.)
Ba=137.33g/mol
N=14.01g/mol
O=16.00g/mol
Add these up
137.33+(28.02+96.00)=261.35g/mol
now multiply the atomic mass by moles.
261.35*9=2352.15g or 2.4kg(significant digits)
I hope this helps