Explanation

[Solution by Dr. Abubacker] CFSE is zero for high-spin $d^5$ ($t_{2g}^3e_g^2$). Fe³⁺ ($d^5$) with the weak-field ligand SCN⁻ is high spin, so CFSE $=0$. Fe³⁺ with en is low spin (non-zero CFSE), and the other two are Fe²⁺ ($d^6$) complexes. Answer (4).