Question

Yasmeen wrote a few series of hydrocarbons and left blanks in between. Look at the chemical formula in the series of hydrocarbons carefully. Answer the following questions accordingly.

I	II	III
$C{{H}_{4}}$	${{C}_{2}}{{H}_{4}}$	X
${{C}_{2}}{{H}_{6}}$	${{C}_{3}}{{H}_{6}}$	${{C}_{3}}{{H}_{4}}$
Y	${{C}_{4}}{{H}_{8}}$	${{C}_{4}}{{H}_{6}}$
${{C}_{4}}{{H}_{10}}$	Z	${{C}_{5}}{{H}_{8}}$

X and Y respectively are:
A) ${{C}_{2}}{{H}_{2}}$ and ${{C}_{3}}{{H}_{8}}$
B) ${{C}_{2}}{{H}_{2}}$ and ${{C}_{4}}{{H}_{10}}$
C) ${{C}_{2}}{{H}_{2}}$ and ${{C}_{3}}{{H}_{6}}$
D) ${{C}_{2}}{{H}_{4}}$ and ${{C}_{3}}{{H}_{8}}$

Answer 1

Hint The answer to this question is based on the general concept of denoting a hydrocarbon which involves the general formula used for the notation like ${{C}_{n}}{{H}_{2n+2}}$, ${{C}_{n}}{{H}_{2n-2}}$ and so on. The answer will be obtained with the help of this fact.

Complete step – by – step answer:
From the previous chapters of organic chemistry that is from the chapter named hydrocarbons, we have studied how to write the hydrocarbons in terms of molecular formula and also relating notations.
Now, we shall see what type of the compounds are given in the table above and how we can find the values of X and Y.
- We know that hydrocarbons can be denoted in the general form assigned for different types of hydrocarbons like alkanes, alkenes and other functional groups including compounds.
- The molecular formula of such compounds is divided accordingly and are given separate general formulas to identify them.
- The examples include, the general formula given for the alkynes that i one triple bond between them is ${{C}_{n}}{{H}_{2n-2}}$
In the similar way for different types of compounds, different general formulas are given.
Now, in the above table given, column I has the letter Y and in this column, if we observe carefully, the compounds present are alkanes with the general formula ${{C}_{n}}{{H}_{2n+2}}$
Therefore, for Y, if we put n = 3, we get Y =${{C}_{3}}{{H}_{8}}$
Similarly, the value of X to be found is in column III and therefore, if we observe this column carefully, it has the general form of alkynes which is given by., ${{C}_{n}}{{H}_{2n-2}}$
Therefore, if we put n = 2 then we will get X = ${{C}_{2}}{{H}_{2}}$

Hence, the correct answer is option A) ${{C}_{2}}{{H}_{2}}$ and ${{C}_{3}}{{H}_{8}}$

Note: You should be thorough with some of the general formulas used to indicate different types of hydrocarbons present and also some of the basic formulas which have the common functional groups like aldehydes, esters and so on and this will lead you to guess the correct answer.