A solution has 4.35 g of potassium sulphate, K₂SO₄, of molar mass 174 g/mol, in 500 g of water…

Step 1. Molality. $\dfrac{4.35}{174} = 0.0250\ \text{mol}$ in $0.500\ \text{kg}$, so $m = 0.0500\ \text{mol/kg}$.

Step 2. The fall if nothing split. $1.86\ \text{K kg/mol} \times 0.0500\ \text{mol/kg} = 0.0930\ \text{K}$.

Step 3. The factor. $i = \dfrac{0.238\ \text{K}}{0.0930\ \text{K}} = 2.56$.

Step 4. The degree of dissociation. We want $\alpha$, so $\alpha = \dfrac{i - 1}{\nu - 1} = \dfrac{1.56}{2} = 0.78$.