Answer:
(C) Oxygen because it has the strongest attractive force and the largest
electronegativity
Explanation:
Oxygen will be most reactive
configuration = 
As oxygen need only two electrons to complete its octet.
Oxygen will have stronger force than nitrogen as it will tend to pull electrons more to complete its octet. Also along the period electronegativity increases so oxygen has higher electronegativity than nitrogen
Answer:
The area around the nucleus must be of low mass.
Explanation:
Rutherford`s experiment showed that there are some positive charges in the center of the atoms, and because they are all together, they will give a great mass to the atom.
It was quite different from Thomson`s experiment, in which it was thought that the negative charges were mixed with the positive charges, around the atom (like a Pudding Model). In Rutherford`s experiment, because the direction of beta particles, it was the prediction of the positive nucleus.
Hope this info is useful.