To determine the number of molecules in a 4.85 g sample of dimethylmercury, we need to calculate the number of moles in the sample and then multiply that by Avogadro's number (6.022 x 10^23 molecules/mole). Here are the steps:

1. Calculate the molar mass of dimethylmercury (CH3)2Hg:

C: 12.01 g/mol x 2 = 24.02 g/mol

H: 1.01 g/mol x 6 = 6.06 g/mol

Hg: 200.59 g/mol

Total molar mass = 24.02 g/mol + 6.06 g/mol + 200.59 g/mol = 230.67 g/mol

2. Calculate the number of moles in the 4.85 g sample:

Moles = Mass / Molar mass

Moles = 4.85 g / 230.67 g/mol

Moles = 0.0210 mol

3. Calculate the number of molecules in 0.0210 mol of dimethylmercury:

Molecules = Moles x Avogadro's number

Molecules = 0.0210 mol x 6.022 x 10^23 molecules/mol

Molecules = 1.27 x 10^23 molecules

Therefore, the 4.85 g sample of dimethylmercury contains approximately 1.27 x 10^23 molecules.