Fill in the missing number, assuming that the carbons are single-bonded to each other:
C2H3Cl?
The missing number represents the number of hydrogen atoms bonded to the carbon atoms in the molecule C2H3Cl.
To determine the missing number, we can use the fact that each carbon atom requires four bonds in order to satisfy its valency. However, the given molecule only contains one chlorine atom, which has a higher electronegativity than carbon and forms only one bond.
Therefore, the carbon atoms must share the remaining bonds amongst themselves. Since there are two carbon atoms in the formula, they must share three bonds between them. This means that each carbon atom is bonded to two hydrogen atoms and to each other.
Thus, the missing number is 2. The molecular formula is C2H3Cl2.