To calculate the molarity (M) of a solution, you can use the formula:
\[ \text{Molarity (M)} = \frac{\text{moles of solute}}{\text{liters of solution}} \]
In this case, you have 0.85 mol of MgCl₂ and a solution volume of 1.5 L.
Plugging in the values:
\[ \text{M} = \frac{0.85 , \text{mol}}{1.5 , \text{L}} = 0.5666667 , \text{M} \]
Now, we need to round this value according to the significant figures. The number of significant figures is determined by the values used in the calculation. The value 0.85 has 2 significant figures and 1.5 has 2 significant figures as well. Therefore, we will round our result to 2 significant figures.
Thus, rounding 0.5666667 to 2 significant figures gives:
\[ \text{M} = 0.57 , \text{M} \]
So, the molarity of the solution is 0.57 M.