Question

The formula of ethyne is:
A. ${{C}_{2}}{{H}_{2}}$
B. ${{C}_{6}}{{H}_{6}}$
C. ${{C}_{2}}{{H}_{4}}$
D. ${{C}_{2}}{{H}_{6}}$

Answer 1

Hint: Start this question by breaking the given compound into two parts. Try to identify the number of carbons in the compound. The first half suggests the number of carbon present in the compound and the second part suggests the number and kind of bond present between the carbon.

Complete step-by-step solution -

As the name suggests, ethyne is made up of eth + yne. The term “eth” indicates two carbon compounds and “yne” indicates that it is an alkyne, i.e. it has a triple bond. Ethylene is the simplest alkylene.
The prefixes are given in the table below –

Number of Carbons	Prefix
1	Meth-
2	Eth-
3	Prop-
4	But-
5	Pent-
6	Hex-
7	Hept-
8	Oct-
9	Non-
10	Dec-
11	Undec-
12	Dodec-

The suffix -ane, -ene and -yne indicate the presence of single bond, double bond and triple bonds respectively.
The structure of ethyne is as given below -
$HC\equiv CH$
As we can see from the structure, the number of carbons and hydrogens in ethyne is 2.
Therefore, the answer is option (a) – ${{C}_{2}}{{H}_{2}}$.
${{C}_{2}}{{H}_{4}}$

Additional information:
Ethylene is also known as Acetylene. Also, as we can see from the structure, all four atoms are in the same line. The bond angle is approximately $180{}^\circ C$. Therefore, the shape of this molecule is linear and its hybridization is $s{{p}^{2}}$.

Note: Nomenclature in organic chemistry is very easy. The hydrocarbons with a single bond are called alkanes. Similarly, hydrocarbons with double bonds are called alkenes and hydrocarbons with triple bonds are called alkyne.