Final answer:
Without additional context, it is not possible to accurately identify (z) in a reaction series involving CH₄. Understanding the particular reactions or the progression in a series of hydrocarbons could help pinpoint (z).
Step-by-step explanation:
The question asks us to identify (z) in a reaction series. There might be a possible typo or missing context, as (z) isn't clearly defined with the information provided. To identify products and reactants in a chemical reaction, we should start with known chemical substances and their reactions with other compounds. For instance, if we consider CH₄ (methane), we could discuss its reaction with other substances or its derivatives. A reaction example involving methane is its combustion, which typically forms CO₂ (carbon dioxide) and H₂O (water):
CH₄ + 2O₂ → CO₂ + 2H₂O
For reactions with hydrocarbons like CH₄, addition reactions with halogens, substitution reactions with other substituents, or reforming reactions to produce longer hydrocarbon chains might apply. We can also consider the complete series from methane (CH₄) to other alkanes of increasing carbon number, for instance, ethane (C₂H₆), propane (C₃H₈), up to octane (C₈H₁₈) listed in the example data provided. The precise identification of (z) requires additional context about the types of reactions or the series being studied.