What is the formula of the product formed when $F^{-}$ reacts with enamel on teeth?

Correct statements among $(i)$ to $(iv)$ regarding silicones are:
$(i)$ they are polymers with hydrophobic character
$(ii)$ they are biocompatible
$(iii)$ in general,they have high thermal stability and low dielectric strength
$(iv)$ usually they are resistant to oxidation and used as greases.

In which of the following sets are allotropes of carbon correctly matched with their uses?
$i$. graphite - crucibles
$ii$. activated charcoal - water filters
$iii$. carbon black - fuel
The correct answer is

Which one of the following is present in the chain structure of silicates?

Which of the following elements does not form a monoxide?

The number of six-membered and five-membered rings in Buckminster fullerene respectively is