An aqueous solution of an unknown quantity of a nonelectrolyte solute is found to have a freezing point of −0.58°c. what is the molal concentration of the solution?

Depression in freezing point is a colligative property i.e. it depends upon under  of solute particles present in solution.

Depression in freezing point (ΔTf) is mathematically expressed as,
ΔTf = Kf X m        (1)
where Kf = cryoscopic constant
m = molality of solution

If solvent used is water, Kf = 1.853 K Kg/mol and Freezing point of pure solvent = 0 oC
∴ΔTf = 0.58 K          (2)
Substituting 2 in 1 we get
0.58 = 1.853 X m
∴ m = 0.313 m

Thus, molality of solution is 0.313 m