Question

Consider the following statements:
Statement - I: In three dimensional network of \(SiO_2\), if few Si atoms are replaced by Al atoms, the resulting structure acquires a positive charge.
Statement - II: Silicones are organo - silicon polymers which have \((R_2SiO)\) as a repeating unit.

• A. Both statements - I and II are correct
• B. Statement - I is correct but Statement - II is not correct
• C. Statement - I is not correct but Statement - II is correct
• D. Both statements - I and II are not correct

Hint:

Aluminum in silicate networks creates negative charges (aluminosilicates), which must be balanced by cations like \(Na^+\) or \(Ca^{2+}\).

Answer 1

The Correct Option is C

Step 1: Read both statements.
Statement I says replacing some Si by Al in an $SiO_2$ network gives a positive charge. Statement II says silicones repeat the unit $(R_2SiO)$.
Step 2: Look at the charges in Statement I.
In the silica framework silicon is $Si^{4+}$. Aluminium enters as $Al^{3+}$, which carries one less positive charge per substitution.
Step 3: Decide the net charge.
Swapping a $+4$ ion for a $+3$ ion leaves the framework short of positive charge, so the structure becomes negatively charged, not positive. Statement I is therefore incorrect.
Step 4: Examine Statement II.
Silicones are organosilicon polymers, and their backbone really is built from the repeating unit $(R_2SiO)_n$.
Step 5: Verify Statement II.
That repeating unit is exactly the standard description, so Statement II is correct.
Step 6: Combine.
Statement I incorrect, Statement II correct, which is option 3.
\[ \boxed{\text{Statement - I is not correct but Statement - II is correct}} \]