Explain the effect of `SN^2` rates for the following reactions :
(a) Increasing the polarity of solvent.
(b) Show the `T.S` with all partial charges for each reaction type.
(I) `Me_2 overset (oplus) S - Me + NH_3 rarr Me overset (oplus)N H_3 + Me_2 S`
(II) `Me I + NH_3 rarr Me overset (oplus)N H_3 + I^(Ө)`
(III) `Me I + overset (Ө) O H rarr Me OH + I^(Ө)`
(IV) `Me_2 S^(oplus) - Me + overset (Ө) OH rarr Me OH + Me_2 S`.

Explanation

To explain the effect of increasing the polarity of the solvent on the SN2 reaction rates for the given reactions, we will analyze each reaction step by step, including the transition states and their partial charges.

### Step-by-Step Solution:

#### (a) Effect of Increasing Polarity of Solvent on SN2 Rates:

1. **Reaction I: \( \text{Me}_2\overset{+}{S} - \text{Me} + \text{NH}_3 \rightarrow \text{Me}\overset{+}{N} \text{H}_3 + \text{Me}_2 S \)**
- **Mechanism**: The nucleophile (NH3) attacks the electrophilic carbon attached to the sulfonium ion (Me2S+).
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