Final answer:
Without specific activity coefficient data for Fe at different ionic strengths, the exact activity coefficient at an ionic strength of 0.035 M cannot be interpolated or calculated.
Step-by-step explanation:
To calculate the activity coefficient of Fe in a solution with an ionic strength of 0.035 M, you would typically need to refer to tables that provide the activity coefficients for various ions at different ionic strengths. However, specific provided details are related to solubility products, the van 't Hoff factor, and complex ion formation rather than directly providing information for the calculation of activity coefficients.
Linear interpolation might be employed by finding the activity coefficients at ionic strengths surrounding 0.035 M, and then calculating the specific coefficient at 0.035 M. Unfortunately, without the specific activity coefficient data for Fe at two different ionic strengths, the exact value cannot be interpolated. More data or a reference to such a table would be needed to complete this calculation.