MgCl2
Mg=24
Cl=35.5×2 = 71
rmm= 71+24=95g
1 mole = molar mass
1 mole = 95g
1g = 1/95 moles
345g= 1/95 × 345
3.6 moles
Answer: Concentration of the chemist's sodium chloride solution is 34.4 mol/L.
Explanation:
Molarity of a solution is defined as the number of moles of solute dissolved per Liter of the solution.

where,
n= moles of solute
= volume of solution in ml
Given : moles of
= 6.89
volume of solution = 200 ml
Putting in the values we get:

Thus the concentration of the chemist's sodium chloride solution is 34.4 mol/L.
Density = mass/volume
Density = 81g/0.9cm³
Density = 90g/cm³
: )