The mass (g) of barium chloride (BaCl2) with the amount of a substance in 1.5 mol is …

m = M * n.
where m is the desired mass of barium chloride, M is the molar mass of barium chloride, n is the amount of chloride substance.
n is given in the problem statement and is equal to 1.5 mol.
We find the molar mass of chloride according to the periodic table. To do this, add up the atomic masses of all components of the substance: 233 + 35.5 * 2 = 304.
By multiplying the molar mass by the amount of barium chloride substance, we find the mass: 304 * 1.5 = 456g – the answer.