Assertion `:` Tropylium cation is aromatic in nature
Reason `:` The only property that determines its aromatic behaviour
is its planar structure.

Options

A. Statement-I is True, Statement-II is True : Statement-II is a correct explanation for Statement-I
B. Statement-I is True, Statement-II is True : Statement-II is `NOT` a correct explanation for Statement-I
C. Statement-I is True, Statement-II is False.
D. Statement-I is False, Statement-II is True.

Answer

To solve the assertion-reason question regarding the tropylium cation, we will analyze both the assertion and the reason step by step.

### Step 1: Understanding the Assertion
The assertion states that the tropylium cation is aromatic in nature.

- **Aromaticity Criteria**: For a compound to be aromatic, it must satisfy the following criteria:
1. It must be cyclic.
2. It must be planar.
3. It must have a continuous overlap of p-orbitals (conjugation).
4. It must follow Huckel's rule, which states that it should have \(4n + 2\) π electrons, where \(n\) is a non-negative integer.

### Step 2: Analyzing the Structure of Tropylium Cation
The structure of the tropylium cation can be represented as a cyclic compound with a positive charge.

- **Hybridization**: In the tropylium cation, all carbon atoms are sp² hybridized. This hybridization allows for the formation of π bonds and ensures that the compound is planar.
- **Cyclic and Planar**: The structure is indeed cyclic and planar, fulfilling two of the aromaticity criteria.

### Step 3: Counting π Electrons
Now, we need to check the number of π electrons in the tropylium cation.

- **Double Bonds**: The tropylium cation has three double bonds, contributing a total of 6 π electrons (2 electrons from each double bond).
- **Huckel's Rule**: The total π electron count of 6 fits Huckel's rule since \(n = 1\) gives \(4(1) + 2 = 6\).

### Step 4: Conclusion on Aromaticity
Since the tropylium cation is cyclic, planar, has continuous p-orbital overlap, and contains 6 π electrons, we conclude that:

- **Assertion**: True (Tropylium cation is aromatic).

### Step 5: Understanding the Reason
The reason states that the only property that determines its aromatic behavior is its planar structure.

- **Analysis of the Reason**: While a planar structure is necessary for aromaticity, it is not the only factor. The presence of a cyclic structure and the appropriate number of π electrons (following Huckel's rule) are also critical for determining aromaticity.

### Final Conclusion
- **Assertion**: True
- **Reason**: False

Thus, the correct answer is that the assertion is true, but the reason is false.