1.as you move from left to right across a period, the number of valence electrons
-increases
-stays the same
-increases and then decreases
-decreases
2.compared with group 2a elements, group 64 elements have
-more atoms in the ground state
-more valence electrons
-more isotopes
-fewer valance electrons
3.which of the following group 7a elements is the most reactive?
-ci(chlorine
-i(iodine)
-f(fluorine)
-br(bromine)

1. The number of valence electrons increases as you go from left to right across a period. This is because the number of electrons increases, so another electron will be added to the outer shell.

2. Group 6A elements will have 6 valence elecrons, while Group 2A elements only have 2, therefore Group 6A elements have more valence electrons that Group 2A elements.

3. Fluorine has a smaller atomic size than the other halogens (Cl, Br, I), so its valence electrons are nearer to its nucleus. This means that the attractive forces are stronger, so when another electron (from another atom) draws near the F atom, it is more likely that the electron will be pulled toward the nucleus and react with the F atom.