To calculate the number of molecules in a 6.30g sample of dimethylmercury, we can use the following formula:

```

Number of molecules = (Mass of sample in grams) / (Molar mass of compound in grams/mole) × Avogadro's number

```

The molar mass of dimethylmercury (CH3)2Hg is 236.57 g/mol. Avogadro's number is 6.022 × 10^23 molecules/mol.

Substituting the given values into the formula, we get:

```

Number of molecules = (6.30 g) / (236.57 g/mol) × (6.022 × 10^23 molecules/mol)

```

```

Number of molecules ≈ 1.59 × 10^22 molecules

```

Therefore, a 6.30g sample of dimethylmercury contains approximately 1.59 × 10^22 molecules.