2 cylinders inline in bike like er6n, zzr 250 are 4 stroke bikes.

for best comparison,
zx2r has 4 cylinders inline. 4 stroke engine.
zzr 250 has 2 cylinders, also a 4 stroke engine.

regarding the technical things, i cant really explain as i do not understand that much either.
But the basic rule is that 4 cylinders are better than 2. In terms of speed and acceleration.

Usually there are no 2 stroke bike larger than 250cc. There are some exceptions though.

another odd thing that you might want to know. BMW are producing SINGLE cylinder bikes of 600cc above.

Lower cylinders are better at travelling very very very long distance which makes bike like zzr 250 better than zx2r when long distance travel is concerned.