A polymer chemist studies two reactions, P and Q. The table gives information about the starting molecules and one repeating unit of each polymer.
| Reaction | Starting molecule(s) | Functional group information | Formula of one repeating unit |
|---|---|---|---|
| P | One molecule with formula C4H8\text{C}_4\text{H}_8C4H8 | Contains a C=C\text{C}=\text{C}C=C bond | C4H8\text{C}_4\text{H}_8C4H8 |
| Q | Molecule X, C4H10O2\text{C}_4\text{H}_{10}\text{O}_2C4H10O2, and molecule Y, C2H2O4\text{C}_2\text{H}_2\text{O}_4C2H2O4 | X has an OH\text{OH}OH group at each end; Y has a COOH\text{COOH}COOH group at each end | C6H8O4\text{C}_6\text{H}_8\text{O}_4C6H8O4 |
A chemist considers two candidates to replace X in reaction Q.
| Candidate | Structure |
|---|---|
| A | HO-CH2-CH2-OH\text{HO-CH}_2\text{-CH}_2\text{-OH}HO-CH2-CH2-OH |
| B | CH3-CH2-OH\text{CH}_3\text{-CH}_2\text{-OH}CH3-CH2-OH |
Explain, using the data, why one repeating unit from reaction P contains the same atoms as its monomer but one repeating unit from reaction Q does not. Use the formulae to determine the number of water molecules equivalent to the atoms missing from one repeating unit of Q.
Which candidate could replace X while allowing reaction Q to form a long polymer chain? Justify your choice using the structures.