Which allotrope of carbon is isomorphous with crystalline silicon?

Which of the following does not exist?

Which one of the following statements about the zeolites is false?

What is aluminosilicate? Which ions are used to balance its electric charge?

Assertion : $Pb^{4+}$ compounds are stronger oxidizing agents than $Sn^{4+}$ compounds.
Reason : The higher oxidation states for the group $14$ elements are more stable for the heavier members of the group due to 'inert pair effect'.

How many corners of $SiO_4$ units are shared in the formation of three dimensional silicates?