For the following groups given below the correct decreasing order of leaving group power in can be given as (1) \(-\mathrm{OCH}_{3}\) (2) \(-\mathrm{OAC}\) (3) \(-\mathrm{O}-\mathrm{SO}_{2}-\mathrm{CF}_{3}\) (4) \(-\mathrm{O}-\mathrm{SO}_{2}-\mathrm{me}\) (a) \(1>3>4>2\) (b) \(3>4>1>2\) (c) \(3>4>2>1\) (d) \(3>2>4>1\)

Substitution reactions are fundamental chemical processes where an atom or a group of atoms in a molecule is replaced by another atom or group. This replacement can occur through various mechanisms; the most common ones being the Sn1 and Sn2 mechanisms.

In Sn1 reactions, the leaving group departs before the new group attaches, forming an intermediate carbocation. This reaction is dependent on the stability of the carbocation and therefore favors tertiary carbocations.

Sn2 mechanisms, on the other hand, involve a simultaneous exchange where the leaving group is pushed out as the incoming group attacks. This is a single-step process with a transition state, and it typically occurs in primary substrates due to steric hindrance.

The leaving group's ability to leave and the nucleophile's strength to attack are paramount in substitution reactions. A good leaving group will effortlessly break away from the main molecule, leading to a more successful substitution reaction.

Elimination reactions involve the removal of two atoms or groups from adjacent carbon atoms, resulting in the formation of a double bond. These reactions are categorized mainly as E1 or E2.

E1 reactions follow a two-step mechanism where the leaving group exits first, followed by the deprotonation of the adjacent carbon atom, leading to a double bond. These reactions favor more substituted carbons since they can better stabilize the carbocation intermediate.

E2 reactions happen in a single concerted step where the base removes a proton from the β-carbon as the leaving group departs. The strength of the base and the ability of the leaving group to leave are crucial for the rate of E2 reactions.

The proficiency of a leaving group in elimination reactions is similar to substitution reactions: better leaving groups facilitate the elimination process, making it faster and more favorable.

Resonance stabilization is a concept which refers to the delocalization of electrons within a molecule through p orbitals, allowing the molecule to adopt multiple structures that contribute to the overall stability of the system.

In the context of leaving groups, resonance stabilization plays a vital role. A leaving group that can delocalize its negative charge over a larger volume through resonance is inherently more stable and thus a better leaving group.

For example, groups attached to a benzene ring or groups with electronegative atoms capable of accepting additional electron density (e.g., the sulfonyl group in methanesulfonate and trifluoromethanesulfonate) are excellent leaving groups. The stability these groups achieve through resonance makes it easier for them to depart during chemical reactions, thus speeding up the reaction rate.