Which formula represents an alkane?

(1) C2H2

(2) C2H4

(3) C3H4

(4) C3H8

Answer and Explanation: The general formula for an alkane is CnH2n+2. Therefore all we need to do is plus the carbon subscript and find out how many hydrogens are needed to make the formula an alkane. Let's start with choice 1: C2H2, If we plug in 2 for n, we see H must be 2*2+2=6.

2: C2H4, the number of Hydrogens is still not 6 and is therefore not a correct answer choice.

3. C3H4, if we plug in 2 for n, we see that H must be 2*3+2 = 8

4. C3H8, the number of Hydrogens is 8 which is the correct answer.

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