Among the following,which is the best description of water in the solid phase?

Covalent molecules are usually held in a crystal structure by

$PBr_{5(s)} \rightarrow PBr_{4}^{+} + Br^{-}$
$Br^{-} + Br_2 \rightarrow Br_{3}^{-}$
Which of the following forces is responsible for the interaction of $X^{-}$ and $X_2$ to form a coordinate bond between $X^{-}$ and $X_2$?

The compound,found in nature in gas phase but ionic in solid state is

Dry ice is an example of

Which one of the following substances consists of small discrete molecules?