Question

Which of the following does not belong to the same homologous series?
$(1)\,{C_4}{H_{10}}\,\,(2)\,{C_2}{H_6}\,\,(3)\,{C_3}{H_8}\,\,(4)\,{C_4}{H_8}$
A.$1$
B.$2$
C.$3$
D.$4$

Answer 1

We are solving all above formulas according to the three homologous series we have, alkane alkenes and alkynes. As you have known that each type of hydrocarbon has its general formula and if we put the value of $n = \,1,2,3........\,so\,on$ we get different hydrocarbons of these. Alkane has its series where any two hydrocarbons differ by $- C{H_2}\,unit\,or\,(14)\,amu$ . Try to find out the odd one.

Complete step-by-step answer: Hydrocarbons are compounds of carbon and hydrogen, the carbon can make bonds as single, double or triple bonds. If during catenation property by which carbon makes covalent bond with other carbon, if during catenation a single bond is formed then hydrocarbon is called as alkanes. The general formula of alkanes are ${C_n}{H_{2n + 2}}$ similarly for alkene the general formula is ${C_n}{H_{2n}}$ and al last for alkynes ${C_n}{H_{2n - 2}}$ . Now among the four options we have to find out which type of hydrocarbon is these.
As the first option of ${C_4}{H_{10}}$ here if we put $n = 4$ for carbon atoms, we have to get $10$ hydrogens and we will get this type if we consider the general formula of alkanes. This option $1$ is an alkane. Next we have, ${C_2}{H_6}$ for this if we put the number of carbon atoms as $2$ then hydrogens must be $6$ it is also an alkane. Now coming to third hydrocarbon which is ${C_3}{H_8}\,\,$ it means for this hydrocarbon, we have to put the carbon atoms as $3$ and then to maintain hydrogens as $8$ we have to put it in general formula of alkane, it means it is also an alkane. Lastly we have ${C_4}{H_8}$ . This is different if you try to make this formula form a general formula of alkane, this cannot be achieved by that. So, for this formula we have to put the number of carbon atoms as $4$ in the general formula of alkene then we will get hydrogen as $8$ .

The different one is option $(4)$.

Note: Don’t mistake all the three types of hydrocarbon as one, it means among four three are of one type it may be alkane, alkene or alkynes. So, we have to find the odd one. For making a molecular formula you just have to put the value of n in any of the general formulas and you will get three types of hydrocarbons alkane, alkene and alkyne. One among them must be your answer.