Can electrons be present outside orbitals. If yes how does this affect chemical reactions In my physical chemistry textbook it is written (Or typed) that orbitals are regions where probability of finding electron is high (90%-100%). But since orbitals are regions of probability is it possible for electrons to be present outside orbitals for just a small number of atoms in a reaction if so how does this affect reactions that take place with these small number of atoms
There are more levels of abstraction involved. At first, orbitals are simplification and they are best described as "one electron wavefunction", ie. area of space where one electron can reside (or two, if you think of spatial orbitals, as opposed to spin-orbitals). 

Being expressed as a wavefunction, the orbital (and therefore electron residing in it) has nonzero probability in whole space (I mean, whole universe). But the probability decays very fast. 

If you plot a probability density, see image below, you can clearly see the behaviour. If, on the other hand, want to plot the 3d surface, which are often shown in textbooks, you have to state some cutoff value. Often it is probability density of 0.9, ie. 90%. By this you obtain the typical pictures of orbitals.



I would deliberately leave your question without answer, as they stem from severe confusion caused by your textbook.