Which of the following species exhibits a perfectly linear shape? — Chemical Bonding Chemistry Question

💡 Solution & Explanation

The triiodide ion ($I_3^-$) features an $sp^3d$ hybridized central iodine atom. With 2 $\sigma$ bonds and 3 lone pairs, the lone pairs occupy the three equatorial positions to minimize $lp-lp$ repulsions at $120^\circ$, leaving the two terminal iodine atoms in the axial positions, yielding a linear shape ($180^\circ$). The other molecules are bent/V-shaped.