AIIMS 2006 Chemistry Silicones Assertion Reason Question

To analyze the assertion and reason provided in the question about silicones, we need to break down each component:

Assertion:

Silicones are hydrophobic in nature.

Explanation: Silicones are polymers that contain a backbone of alternating silicon (Si) and oxygen (O) atoms, typically represented as the repeating unit $[-Si-O-]$. The structure of silicones results in their hydrophobic characteristics due to the large silicon-oxygen bond which does not easily interact with water molecules. Furthermore, the organic groups (such as methyl or phenyl) that may be attached to the silicon contribute to the non-polar nature of silicones, making them repel water, thus confirming that silicones are indeed hydrophobic.

Reason:

Si–O–Si linkages are moisture sensitive.

Explanation: While it is true that Si–O bonds do exhibit some sensitivity to moisture, this sensitivity mainly refers to the reactivity of silicon compounds. In the presence of moisture, silicones can undergo hydrolysis, which can lead to degradation or changes in the structure. However, the moisture sensitivity of the Si–O–Si linkages does not inherently explain why silicones are hydrophobic. In fact, their hydrophobic nature is more related to their overall molecular structure and the presence of non-polar groups rather than the sensitivity of the Si–O–Si linkages to moisture.

Conclusion:

• The assertion is true: Silicones are indeed hydrophobic in nature.
• The reason is false as it does not accurately explain the assertion; the Si–O–Si linkages' moisture sensitivity does not directly contribute to the hydrophobic characteristic of silicones.

Thus, the correct answer is C) if assertion is true, but reason is false.

Why Other Options Are Incorrect:

• Option A: This option states that both the assertion and the reason are true, and that the reason correctly explains the assertion. This is incorrect because the reason is false.
• Option B: This option states that both assertion and reason are true but that the reason does not explain the assertion. This is incorrect because the reason is not true at all.
• Option D: This option states that both the assertion and reason are false. This is incorrect because the assertion is true.

Summary:

In summary, silicones are hydrophobic due to their molecular structure, while the Si–O–Si linkages being moisture-sensitive does not provide a valid explanation for this property. Therefore, we conclude that the correct answer is C.