what is the molarity of an antifreeze solution glycol in water containing 15.4 g of ethylene glycol (HOCH2CH2OH) and 84.6 g H2O ?

Surely you mean molality and not molarity.

mols eth glycol = grams/molar mass
Then m = molality = mols/kg solvent.

To calculate the molarity of a solution, you need to know the number of moles of the solute (ethylene glycol, in this case) and the volume of the solution (in liters) that contains the solute.

To find the number of moles of ethylene glycol, you'll need its molar mass. The molar mass of ethylene glycol (C2H6O2) is:
(2 * 12.01 g/mol for carbon) + (6 * 1.01 g/mol for hydrogen) + (2 * 16.00 g/mol for oxygen) = 62.07 g/mol

Divide the mass of ethylene glycol by its molar mass to get the number of moles:
15.4 g / 62.07 g/mol = 0.2485 mol

The volume of the solution is not given in the question. Therefore, you cannot calculate the molarity without knowing the volume of the solution. Molarity is defined as moles of solute per liter of solution.

If you have the volume of the solution, divide the number of moles of solute by the volume of the solution in liters to get the molarity. For example, if you have 500 mL of the solution (0.5 L):
Molarity = 0.2485 mol / 0.5 L = 0.497 M

Keep in mind that the molarity may vary depending on the volume of the solution.