the number of valence electrons found in an atom from the main group element is equal too

Question

The answer is its group numver, but I wasn't sure why that is. Can someone explain that to me please.

Answer 1

The group number tells you the number of valence electrons, i.e. the number of electrons in the outer shell. This is just tge way tge Periodic table is arranged. The exceptions are the transition elements.  A simple example would be that elements in group 1 have one valence electron; those in group 2 have 2 and so on.