Explain why the following statements are not correct?
i)  All groups contain both metals and non-metals
ii) In group I, reactivity decreases with increases in atomic number
iii) Elements in a period become more metallic with increasing atomic number
iv) Atoms of elements in the same group have the same number of electrons. 

i) All groups do not contain both metals and non-metals. Group I and II contain only metals.
ii) In group I, reactivity increases with increase in atomic number. This is because as the size of the atoms increases, the valence shell electrons can be easily removed.
iii) The metallic character decreases in a period with increase in atomic number. This is because across the period, the size of the atom decreases and the valence shell electrons are held more tightly.
iv) In a neutral atom the number of electrons is equal to the number of protons. In a group the atomic number increases as we move down.