The definition of a transition metal is that it must have an incompleted sub-level in one or more of its oxidation states. As zinc has a completed sub-level at all oxidative states, so it can't be considered a transition metal.
A hypothesis is an experimental question that can later be proven correct or incorrect by scientific evidence.
6.0221367 rounded from the last digit would be 6.022137 but when using it calculations, you should just use 6.022 x 10^23.