1. Calculate the molar mass of ethane (C2H6):

* Carbon (C) has a molar mass of 12.01 g/mol.

* Hydrogen (H) has a molar mass of 1.01 g/mol.

* Molar mass of ethane = (2 * 12.01 g/mol) + (6 * 1.01 g/mol) = 30.07 g/mol

2. Calculate the number of moles of ethane:

* Moles = Mass / Molar Mass

* Moles = 15 g / 30.07 g/mol = 0.50 mol

3. Calculate the number of molecules:

* Avogadro's number (NA) = 6.022 x 10^23 molecules/mol

* Number of molecules = Moles * Avogadro's number

* Number of molecules = 0.50 mol * 6.022 x 10^23 molecules/mol = 3.011 x 10^23 molecules

Therefore, there are approximately 3.011 x 10^23 molecules of ethane in 15 grams of the compound.