The question asks for the composition of alloy when the fraction of alpha ferrite phase is .85. Given options: - .88 wt% C - .255 wt% C - 1.023 wt% C **Approach:** This question relates to the phase diagram of steel and the lever rule for alloy composition. - When the fraction of alpha ferrite (α) is .85, the remaining .15 is the austenite phase. - The composition of the alloy can be estimated using the phase diagram data or lever rule between the two phases. **Using the typical phase diagram data:** - The composition of ferrite (α) phase is approximately .025 wt% C. - The composition of the austenite (γ) phase is approximately .76 wt% C. **Applying the lever rule:** \[ C_{alloy} = f_α \times C_{α} + f_{γ} \times C_{γ} \] Where: - \(f_α = .85\) - \(f_{γ} = .15\) - \(C_{α} \approx .025\) wt% - \(C_{γ} \approx .76\) wt% Calculating: \[ C_{alloy} = (.85 \times .025) + (.15 \times .76) \approx .02125 + .114 \approx .13525 \text{ wt%} \] Since none of the options exactly matches this, the closest option is **.255 wt% C**. --- ### **Correct option:** **.255 wt% C**