What is the general formula for a homologous series?

The general formula for a homologous series provides a way to understand the relationship between the number of carbon atoms and the number of hydrogen atoms in different compounds within that series. In this context, the correct answer highlights the general formula for alkanes, which is CnH2n+2. This formula shows that for every n carbon atoms in an alkane, there are 2n + 2 hydrogen atoms. This structure is consistent across the entire homologous series of alkanes, reflecting their saturated nature—where all carbon atoms are connected by single bonds.

In the case of alkenes, the formula CnH2n is applicable, indicating that each alkene has one less hydrogen atom than the corresponding alkane due to the double bond, which changes the saturation level. For alkynes, the formula CnH2n-2 signifies that there are two fewer hydrogen atoms than in the corresponding alkane because of the presence of a triple bond.

Since all these formulas are indeed correct for their respective homologous series, the option that encompasses all the given formulas accurately confirms the understanding of the nature of hydrocarbons in these series. Thus, the general formula for each type of hydrocarbon in the provided answers is valid