Answer: We need to 120 g of MgO in the beaker and add enough water to reach the 1 L mark.
Explanation:
Molarity of a solution is defined as the number of moles of solute dissolved per liter of the solution.
[tex]Molarity=\frac{n}{V_s}[/tex]
where,
n = moles of solute
[tex]V_s[/tex] = volume of solution in L
moles of [tex]MgO[/tex] = [tex]\frac{\text {given mass}}{\text {Molar mass}}=\frac{xg}{40g/mol}[/tex]
Now put all the given values in the formula of molality, we get
[tex]3M=\frac{x}{40g/mol\times 1L}[/tex]
[tex]x=120g[/tex]
Therefore, we need to 120 g of MgO in the beaker and add enough water to reach the 1 L mark.
