Assertion In case of `(CH_(3))_(3)N` geometry is pyramidal but in case of `(SiH_(3))_(3)N` it is planar
Reasoning The maximum covalency of Si is six but that of `C` is four .

Options

A. If assertion is true but the reason is false
B. If assertion is false but reason is true
C. If both assertion and reason are true and the reason is the correct explanation of assertion
D. If both assertion and reason are true and the reason is not the correct explanation of assertion

Explanation

To solve the question, we need to analyze both the assertion and the reasoning provided.

### Step 1: Analyze the Assertion
The assertion states that in the case of \( (CH_3)_3N \) (trimethylamine), the geometry is pyramidal, while in the case of \( (SiH_3)_3N \) (trihydrosilamine), the geometry is planar.

- **For \( (CH_3)_3N \)**:
- The nitrogen atom is bonded to three methyl groups and has one lone pair of electrons.
- The hybridization of nitrogen in this molecule is \( sp^3 \).
- The presence of the lone pair leads to a trigonal pyramidal shape due to the repulsion between the lone pair and the bonding pairs, which pushes the bonding pairs closer together.

- **For \( (SiH_3)_3N \)**:
- The nitrogen atom is bonded to three silane groups.
- Silicon can utilize its empty \( d \)-orbitals for back bonding with nitrogen.
- The back bonding allows the molecule to adopt a planar structure because the bonding pairs can spread out more evenly in a planar arrangement.

### Step 2: Analyze the Reasoning
The reasoning states that the maximum covalency of silicon is six, while that of carbon is four.

- **Maximum Covalency of Silicon**:
- Silicon has the ability to expand its octet due to the presence of \( d \)-orbitals, allowing it to form more bonds (up to six).
- This is relevant in the case of \( (SiH_3)_3N \) where back bonding occurs.

- **Maximum Covalency of Carbon**:
- Carbon, on the other hand, does not have \( d \)-orbitals and can only form four bonds (hence a maximum covalency of four).
- This is why \( (CH_3)_3N \) cannot exhibit back bonding and remains pyramidal.

### Conclusion
Both the assertion and the reasoning are correct, and the reasoning provides a valid explanation for the assertion.

### Final Answer
- **Assertion**: True
- **Reasoning**: True
- **Explanation**: The geometry of \( (CH_3)_3N \) is pyramidal due to the lone pair on nitrogen, while \( (SiH_3)_3N \) is planar due to back bonding facilitated by silicon's ability to expand its covalency.

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