C-I is weaker than C-O due to size - Iodine is gigantic compared to oxygen
Bond dissociation energy is determined by bond strength --> bond strength is determined by a variety of factors; in general:
1) bond strength of homonuclear diatomic molecules: e.g. H2, N2, O2, F2, Br2, etc.; these have no electronegativity difference, so a more comprehensive definition requires construction of molecular orbital diagrams and then using bond order equation [(# bonding electrons - # anti bonding electrons)/2]; in simpler terms, you basically construct the best possible Lewis diagram with the available valence electrons
2) bond strength of heteronuclear diatomic molecules: e.g. carbon monoxide vs. cyanide, H-F vs. H-Cl vs. H-Br, etc.; here electronegativity MATTERS - in GENERAL, the greater the bond polarity, the stronger the bond; ATOMIC SIZE also matters - larger atoms make weaker bonds
3) bond strengths in more complex molecules (like organic molecules): you have to look at factors IN ADDITION to bond polarity and atomic size; e.g. inductive effects (halogens are withdrawing groups vs. methyls are donating groups), resonance stabilization (you could get ~1.5 bond order for C-O bond in carbonate), steric effects, etc. -- for these kind of molecules they would most likely provide you a table with values, so you wouldn't need to know specific rules
4) ionic solids: for MCAT purposes, use only Coulomb's Law; hard ions (small, highly charged ions) will have greater lattice energies