Assertion : `(CH_(3))_(3)N` geometry is pyramidal but in case `(SiH_(3))_(3)N` it is planar.
Reason :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 reason provided in the statement.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that the geometry of `(CH₃)₃N` (trimethylamine) is pyramidal, while the geometry of `(SiH₃)₃N` (trihydrosilazane) is planar.
- To analyze this, we need to consider the hybridization and molecular geometry of both compounds.

2. **Analyzing `(CH₃)₃N`**:
- In trimethylamine, the nitrogen atom is bonded to three methyl groups (CH₃) and has a lone pair of electrons.
- The presence of the lone pair causes the geometry to be trigonal pyramidal due to the repulsion between the lone pair and the bonding pairs (VSEPR theory).

3. **Analyzing `(SiH₃)₃N`**:
- In trihydrosilazane, silicon is bonded to three hydrogen atoms and one nitrogen atom.
- Silicon can utilize its d-orbitals to form bonds, allowing it to accommodate more than four bonds.
- The geometry of `(SiH₃)₃N` is planar because the bonding involves sp² hybridization, resulting in a trigonal planar arrangement.

4. **Understanding the Reason**:
- The reason states that the maximum covalency of silicon is six, while that of carbon is four.
- This is true because silicon can expand its octet by utilizing its d-orbitals, whereas carbon cannot because it lacks d-orbitals.

5. **Conclusion**:
- Both the assertion and the reason are true.
- However, the reason does not correctly explain the assertion. The assertion about the geometries is primarily due to the presence of a lone pair in nitrogen for `(CH₃)₃N`, while silicon's ability to form a planar structure is due to its capacity to utilize d-orbitals.

### Final Answer:
Both the assertion and the reason are true, but the reason is not the correct explanation of the assertion.

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