Silane is more reactive than `CH_(4)` towards `Nu^(-)` substitution due to :

Options

A. larger size of Si compared to C which facilitating the attack by nucleophile
B. Polarity of `Si-H` bonds is opposite to that of `C-H` bond
C. Availability of vacant 3d orbitals in case to form the reaction intermediate easily for nucleophilic attack
D. `Si-H` bond energy is lower than that of `C-H` bonds

Explanation

To determine why silane (SiH₄) is more reactive than methane (CH₄) towards nucleophilic substitution, we can analyze several key factors that contribute to this difference in reactivity. Here’s a step-by-step breakdown of the reasoning:

### Step 1: Compare the Size of Silicon and Carbon
- **Explanation**: Silicon is larger than carbon due to its position in the periodic table (it is in the third period, while carbon is in the second). The larger atomic size of silicon allows for more spatial accommodation, making it easier for nucleophiles to approach and attack the Si-H bond.
- **Conclusion**: The larger size of silicon facilitates nucleophilic attack.

### Step 2: Analyze the Polarity of Si-H vs. C-H Bonds
- **Explanation**: The Si-H bond is less polar than the C-H bond. In the case of Si-H, the hydrogen is more electronegative compared to silicon, leading to a different electron distribution. This polarity allows silicon to attract electrons from nucleophiles more effectively than carbon does.
- **Conclusion**: The reversed polarity of the Si-H bond compared to the C-H bond enhances the reactivity of silane towards nucleophiles.

### Step 3: Consider the Availability of d-Orbitals
- **Explanation**: Silicon has access to d-orbitals (3d) that can participate in bonding, allowing it to expand its valency beyond four. This property enables silicon to form more complex reaction intermediates with nucleophiles, facilitating the substitution reaction.
- **Conclusion**: The availability of d-orbitals in silicon allows for the formation of stable reaction intermediates, increasing reactivity.

### Step 4: Compare Bond Energies
- **Explanation**: The Si-H bond is weaker than the C-H bond due to the larger size of silicon. Weaker bonds require less energy to break, making it easier for nucleophiles to substitute the hydrogen atom in silane compared to methane.
- **Conclusion**: The lower bond energy of Si-H compared to C-H contributes to the higher reactivity of silane.

### Final Conclusion
All these factors combined—larger atomic size, reversed bond polarity, availability of d-orbitals, and lower bond energy—contribute to the increased reactivity of silane compared to methane in nucleophilic substitution reactions.

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