What is the total no. Of atoms present in 25.0 mg of camphor

Answer 1

mols camphor = grams/molar mass = 25.0/152.24 = approx 0.15 but that's an estimate you should recalculate it.
The number of molecules is 6.02E23 molecules in 1 mol so in 0.15 mols there will be approx 0.15 x 6.02E23 = approx 1E21. The formula is C10H16O. There are 27 atoms in 1 molecule so 27 x 1E21 = approx ?.
Again, you should recalculate each step.