Ncert Exercises & Solutions

Given below are two statements:

Assertion (A):	If aluminium atoms replace a few silicon atoms in three-dimensional network of silicon dioxide, the overall structure acquires a negative charge.
Reason (R):	Aluminium is trivalent while silicon is tetravalent.

1.	Both (A) and (R) are true and (R) is the correct explanation of (A).
2.	Both (A) and (R) are true but (R) is not the correct explanation of (A).
3.	(A) is true but (R) is false.
4.	(A) is false but (R) is true.

Hint: Aluminium outermost shell contains three electrons and silicon contains four electrons.