In basic organic chemistry, which of the following formulas represent hydrocarbons, and which option correctly describes them?

Introduction / Context:
This question tests your understanding of what a hydrocarbon is in organic chemistry. Hydrocarbons are the simplest organic compounds, consisting only of carbon and hydrogen atoms. They form the basis of many fuels and are fundamental building blocks for more complex molecules. Recognising which formulas represent hydrocarbons is essential for classifying organic compounds, predicting their properties, and understanding combustion reactions. Here, you are given three different molecular formulas and asked to identify whether they are hydrocarbons and to choose the correct overall description.

Given Data / Assumptions:
- The formulas presented are C2H6, C3H8, and CH4.
- Option D suggests that all of these are hydrocarbons.
- It is assumed that you know a hydrocarbon contains only carbon and hydrogen atoms, with no other elements present.
- The question focuses on recognition and classification, not on drawing structures or naming the compounds in detail.

Concept / Approach:
The definition of a hydrocarbon is straightforward: it is any compound composed solely of carbon and hydrogen. If a formula contains only the symbols C and H with any whole number subscripts, it is a hydrocarbon. C2H6 is ethane, a two carbon alkane. C3H8 is propane, a three carbon alkane. CH4 is methane, the simplest alkane with a single carbon atom. All three are saturated hydrocarbons belonging to the alkane series. Since each formula contains only carbon and hydrogen, all of them qualify as hydrocarbons, and the collective description “All of the above” is therefore correct.

Step-by-Step Solution:
Step 1: Recall that a hydrocarbon is a compound made up only of carbon and hydrogen atoms. Step 2: Examine C2H6 and note that it contains only carbon and hydrogen, so it is a hydrocarbon (ethane). Step 3: Examine C3H8 and again see that it contains only carbon and hydrogen, so it is a hydrocarbon (propane). Step 4: Examine CH4 and identify it as methane, another compound containing only carbon and hydrogen, making it a hydrocarbon as well. Step 5: Since all three individual formulas are hydrocarbons, the option that correctly describes them is “All of the above.”

Verification / Alternative check:
You can verify this by consulting any organic chemistry or general science textbook that lists common hydrocarbons. They typically list methane (CH4), ethane (C2H6), and propane (C3H8) as the first members of the alkane series, which are saturated hydrocarbons with the general formula CnH2n+2. Substituting n = 1 gives CH4, n = 2 gives C2H6, and n = 3 gives C3H8, confirming that each of these formulas fits the alkane pattern. No other elements such as oxygen, nitrogen, or halogens are present, so their classification as hydrocarbons is clear and widely accepted.

Why Other Options Are Wrong:
Choosing only C2H6, only C3H8, or only CH4 as hydrocarbons would ignore the fact that the others also meet the definition. There is nothing in the formulas that disqualifies any of them from being a hydrocarbon. Since the question is about which of the following is a hydrocarbon and the correct collective description is that all of them are, options A, B, and C are incomplete and therefore incorrect as the final answer. Option D correctly recognises that all listed formulas are hydrocarbons.

Common Pitfalls:
Some students mistakenly think that only gases like methane can be hydrocarbons and may not recognise ethane and propane by their formulas. Others might assume that more complex formulas with higher carbon numbers are not hydrocarbons unless explicitly named. There can also be confusion between hydrocarbons and functionalised organic compounds that contain oxygen or nitrogen. To avoid these issues, always return to the core definition: if a compound contains only carbon and hydrogen atoms, regardless of chain length, it is a hydrocarbon.

Final Answer:
All three formulas, C2H6, C3H8, and CH4, are hydrocarbons, so the correct choice is All of the above.