1.) Gas given off
2.) precipitate formed
3.) large amount of heat given off
4.) Color change
Answer:

Explanation:
We already know that the mass number of an atom is the sum of the number of protons and the number of neutrons.
So, the mass number of this isotope is;
Number of protons = 7
Number of neutrons = 8
Mass number = 7 + 8 = 15
Hence, the isotope is;

The size of atom reduces
Electronic configuration of sodium -
2,8,1
In order to become stable it loses one electron and becomes positive ion.
It's size reduces.