The molar mass of naphthalene is calculated as follows,
10 x (12.01 g/ mol) + 8 x (1.01 g/mol) = 128.12 g/mol
Divide the given mass by the molar mass to determine the number of moles of naphthalene present in the ball.
n = 1.52 g / 128.12 g/mol = 0.01186 mole
Multiply the number of moles to number of moles per mole.
(0.01186 mol) x (6.022 x10^23 molecules / mole) = 7.14 x 10^21 molecules