Where, the masses used are those of nuclei and not of atoms. If we use atomic masses, we have to add 6me in case of 11C and 5me in case of 11B. Hence,
Q=[m(116C)−m(116B)−2me]c2 (Note me has been doubled)
Using given masses, Q = 0.961 MeV.
Q = Ed+Ee+Eν
The daughter nucleus is too heavy compared to e+ and ν, so it carries negligible energy (Ed ≈ 0). If the kinetic energy (Eν) carried by the neutrino is minimum (i.e., zero), the positron carries maximum energy, and this is practically all energy Q, hence, maximum Ee ≈ Q.