What is the freezing point of radiator fluid that is 50% antifreeze by mass?Kf for water is 1.86 ∘C/m.

The freezing point is -30.0°C

Explanation:

Supposing the antifreeze to be ethylene glycol, C2H6O2.

Take a hypothetical sample of 2000 g of radiator fluid.  Then there is 1000 g each of water and ethylene glycol:

(1000 g C2H6O2) / (62.06810 g C2H6O2/mol) = 16.111 mol C2H6O2

So the molality is 16.111 m.

(1.86 °C/m) x (16.111 m) = 30.0 °C change

0°C - 30.0°C = -30.0°C