Relative reactivity involves the fact that different typ of hydrogen show different reactivity for chlorination of alkanes under controlled condition. This can be obtained by heating the alkanes with molecular chlorine in the dark at 300°C, this leads to mixture of mono, di, tri chlorinated products.

The given reactivity of 1° 2° 3° hydrogen is 1:3.8:5. In 2-methyl butane the 1° H are 9, 2° are 2, 3° are 1.

Amount of mono-chlorinated products = No. of hydrogen reactivity

Mono-chlorinated products from 1° H = 9 1 = 9

Mono-chlorinated products from 2° H = 2 3.8 = 7.6

Mono-chlorinated products from 3° H = 1 5 = 5

Total mono-chlorinated products = 9+7.6+5 = 21.6

Yield % for 1° H chlorination = 9×100/21.6 = 41.67%

Yield % for 2° H chlorination = 7.6×100/21.6 = 35.18%

Yield % for 3° H chlorination = 5×100/21.6 = 23.15%