The decomposition of A follows two parallel first order reactions, with K1=1.26×10-4& K2=3.8×10-5 are shown bellow. The percentage distribution of B and C are

For two parallel reactionskaverage=k1+k2  =  1.26×10−4+3.8×  10−5             =1.64×  10−4sec−1The fractional yield of B=kBkav=1.26×10−41.64×10−40.7683⇒76.83%The fractional yield of C=kBkav=0.38×10−41.64×10−4=0.2317⇒23.17%