Question

Among the following one with the highest percentage of chlorine is
A. Chloral
B. Pyrene
C. PVC
D. Gammaxene

Answer 1

Hint: Fraction of chlorine can be found out by the ratio of mass of chlorine to the mass of organic compound. Highest percentage of chlorine refers to the maximum number of chlorine atoms present in a compound.

Complete step-by-step answer: Option A: chloral has formula $CC{l_3}CHO$. There are three chlorine atoms in the compound. Mass of $1$ chlorine atom is $35.5$
Mass of compound $ = 12 + (35.5)3 + 12 + 1 + 16 = 147.5$

Therefore, $\% $chlorine= $\frac{{35.5(3)}}{{147.5}}100$$ = 72.2%$

Option B: pyrene has formula $CC{l_4}$. Thus, the percentage chlorine is given by
$\% $chlorine= $\frac{{35.5(4)}}{{154}}100$$ = 92.2%$

where mass of compound $ = 12 + (35.5)4 = 154$
There are four chlorine atoms in pyrene.

Option C: PVC means polyvinyl chloride. It is a polymer so let us assume there are n number of monomers present in the polymer chain.
It can be represented as \[ - {(C{H_{2}} - CH(Cl) - )_n}\].
$\% $chlorine= $\frac{{35.5(n)}}{{62.5(n)}}100$$ = 56.8%$

Option D: ${C_6}{H_6}C{l_6}$is called gammaxene. It has six number of chlorine atoms
$\% $chlorine= $\frac{{35.5(6)}}{{291}}100$$ = 73.19%$

Option ‘B’ is correct

Note: If we count the number of chlorine atoms, then the percentage of chlorine atoms in PVC would come out to be maximum if the number of monomers is greater than $6$. But the number of chlorine per monomer unit is $1$. Hence, it does not have the largest percentage of chlorine atom.
But then gammaxene should have highest percentage chorine than pyrene because it has $6$ chlorine atoms which is greater than $4$ chlorine atoms in pyrene. But it is not correct. Thus, percentage chlorine cannot be counted using number of chlorine atoms simply. To arrive at the correct answer, it is always right to calculate $\% $ chlorine using the ratio of mass of chlorine to the mass of compound.