The relative reactivity of  and $3°$ hydrogen's towards chlorination is 1 : 3.8 : 5. Calculate the percentages of all monochlorinated products obtained from 2-methylbutane.

The given organic compound is
This compound has 9 primary hydrogen, 2 secondary and one tertiary hydrogen atoms. The relative  and $3°$ hydrogen atoms chlorination is 1:3.8:5. Relative amount of product after chlorination=Number of hydrogen$×$relative reactivity
Total amount of mono chloro product$=9+7.6+5=21.6$
Percentage of $1°$ mono chloro product$=\frac{9}{21.6}×100=41.7%$
Percentage of $2°$ mono chloro product$=\frac{7.6}{21.6}×100=35.2%$
Percentage of $3°$ mono chloro product$=\frac{5}{21.6}×100=23.1%$