Consider the following statement(s) `CH_(3) = X `and `CV_(3) = V`
(i)Which X dimerises bond angle decreases
(ii) Which Y dimerises bond angle increases
i(iii) In X - Y molecule C- C bond length is less than that in Y - Y molecule
(iv) Bond angle is X is greater than in Y Pick the increases statement

Options

A. II,III
B. I,II,III
C. I,IV
D. II,III,IV

Explanation

To solve the given question, we need to analyze the statements regarding the dimerization of two radicals, CH3 (denoted as X) and CF3 (denoted as Y). We will evaluate each statement step by step.

### Step 1: Analyze Statement (i)
**Statement:** When X dimerizes, bond angle decreases.

- **Analysis:**
- The CH3 radical (X) has a trigonal planar structure with an sp² hybridization, resulting in a bond angle of approximately 120 degrees.
- When CH3 dimerizes to form C2H6 (ethane), the hybridization changes to sp³, which has a tetrahedral geometry and a bond angle of about 109.5 degrees.
- Since the bond angle decreases from 120 degrees to 109.5 degrees, this statement is **true**.

### Step 2: Analyze Statement (ii)
**Statement:** When Y dimerizes, bond angle increases.

- **Analysis:**
- The CF3 radical (Y) has a tetrahedral structure with an sp³ hybridization, resulting in a bond angle of approximately 109.5 degrees.
- When CF3 dimerizes to form C2F6 (difluoroethane), the hybridization remains sp³, and the bond angle will still be approximately 109.5 degrees.
- Therefore, the bond angle does not increase; it remains the same. This statement is **false**.

### Step 3: Analyze Statement (iii)
**Statement:** In X - Y molecule, C-C bond length is less than that in Y - Y molecule.

- **Analysis:**
- The XY molecule (C2H3F3) has a C-C bond that is influenced by the presence of hydrogen and fluorine.
- The YY molecule (C2F6) has only fluorine atoms, which are highly electronegative and will have shorter bond lengths due to increased s-character in the hybridization.
- Generally, C-C bonds in molecules with more electronegative substituents (like F) are shorter than those with less electronegative substituents (like H). Therefore, the C-C bond length in the XY molecule is likely to be longer than in the YY molecule. This statement is **false**.

### Step 4: Analyze Statement (iv)
**Statement:** Bond angle in X is greater than in Y.

- **Analysis:**
- As established earlier, the bond angle in CH3 (X) is approximately 120 degrees, while the bond angle in CF3 (Y) is approximately 109.5 degrees.
- Therefore, the bond angle in X is indeed greater than in Y. This statement is **true**.

### Conclusion
Based on the analysis:
- Statements (i) and (iv) are true.
- Statements (ii) and (iii) are false.

### Final Answer
The statements that are true are (i) and (iv). The statement that is false and increases is (ii).

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