To find the molality of the solution, we first need to calculate the moles of naphthalene and the moles of benzene.

Moles of naphthalene (C10H8):

molecular weight of C10H8 = 128 g/mol

moles of C10H8 = mass of C10H8 / molecular weight of C10H8

moles of C10H8 = 18.5 g / 128 g/mol

moles of C10H8 = 0.1445 mol

Moles of benzene (C6H6):

molecular weight of C6H6 = 78 g/mol

moles of C6H6 = mass of C6H6 / molecular weight of C6H6

moles of C6H6 = 58.5 g / 78 g/mol

moles of C6H6 = 0.75 mol

Now, we can calculate the molality of the solution:

molality = moles of solute / mass of solvent (in kg)

mass of solvent = 58.5 g = 0.0585 kg

molality = 0.1445 mol / 0.0585 kg

molality = 2.471 mol/kg

Therefore, the molality of the solution containing 18.5 g of naphthalene (C10H8) in 58.5 g benzene (C6H6) is 2.471 mol/kg.