Answer:
1: Negative ions, by gaining electrons to fill the valence shell
Step-by-step explanation:
Nonmetals gain the electron to complete the octet and form anion. Consider the example of halogen.
When it combine with metals it gain the electron from the metal and form anion.
For example:
Sodium chloride is ionic compound. The electronegativity of chlorine is 3.16 and for sodium is 0.93. There is large difference is present. That's why electron from sodium is transfer to the chlorine. Sodium becomes positive and chlorine becomes negative ion. The electrostatic forces develop between bonded atoms.