delta H =A,mean bond enthalpy=A
B. CH4------>C +4H
delta H=B, mean bond enthalpy=B/4
and the correct answer is b, why, and what is the difference between the mean bond enthalpy represented by A and B?
However, this is the total amount of energy required to break all four C-H bonds, and so to find the mean bond enthalpy (i.e. the average bond enthalpy of one C-H bond) you have to divide B by four; you can kind of imagine this as B's units becoming kJ mol-1 bond-1
N.B. As a side note, A doesn't actually represent a correct process, so this is kind of a trick question too