To which block of the periodic table does helium belong?
Blocks in the periodic table should not be mixed up with groups (like noble gases). The reason why Helium is considered a noble gas is because its outermost (and at the same time only) shell is fully occupied by its 2 electrons. When you look at the electron configurations in the PTE you can see that the first element which happens to have an occupied p-orbital is boron. Due to this fact boron also has to be the first p-block element, since the block definition is as follows: 


  An element belongs to the block x, if the electron, which is added in comparison to the previous element (by atomic number), is in an orbital of type x in the ground-state electron configuration of that element. 


Or the fast explanation: Why should helium be considered a p-block element, if it doesn't even have any electron in a p-orbital or any shell including a p-orbital?