For this one u can work out the amount of moles in h2co3 by using moles=mass/mr(of h2co3 is 52)
so 16/62=0.258moles then u use the equation
number of particle = moles × 6.02×10^23
=0.258×6.02 ×10^23
=1.55×10^23 molecules.
hope this helps
