Question

A straight-chain hydrocarbon that has only one double bond in each molecule has the general formula

(1) CnH2n-6 (3) CnH2n
(2) CnH2n-2 (4) CnH2n+2

Answer 1

Answer:- 3)
`C_nH_2_n`

Explanations:-
`C_nH_2_n_-_6` is not a valid formula for an alkane, alkene or alkyne.

`C_nH_2_n_-_2` is the general formula for an alkyne that has a triple bond between carbon atoms. The example for an alkyne is acetylene and it's formula is
`C_2H_2` .

In these general formulas, n is an integer number and for alkene and alkyne the minimum value of n is 2.

Acetylene has two carbons so the value of n for it is 2. If we plug in the value of n in the formula
`C_nH_2_n_-_2` then:

`C_2H_4_-_2`

=
`C_2H_2`

In acetylene, there is a triple bond between the carbon atoms and each hydrogen is bonded to each carbon.

If we plug in n = 2 in the formula,
`C_nH_2_n` then:

`C_2H_4`

It could be written as:

`H_2C=CH_2`

There is a has a double bond between the carbon atoms and two H are bonded to each carbon atom so,
`C_nH_2_n` is the right formula of an alkene.

If we plug in n = 2 in the fourth formula then:

`C_2H_4_+_2`

=
`C_2H_6`

It could be written as
`H_3C-CH_3` , it has a single bond between carbons and so it is an alkane.

Answer 2

The correct answer is option 3. A straight-chain hydrocarbon that has only one double bond in each molecule has the general formula of CnH2n. Alkenes are organic compounds which contains C=C bond. Examples are C2H4, C3H6, C4H8.