Question

how and when hallide ions areformed also illustrate with an example?

Answer 1

Dear student!
Halide ion is a halogen atom bearing a negative charge as: X^-1 like F^-, Cl^- , Br^- etc

These, ions are formed when the halogens come in contact with an electropositive or a comparatively less electronegative element which could donate an electron to the X atom so that it first forms a halide ion which further combines as:

Na -> Na⁺ + e^-

Cl + e^- -> Cl^- (chloride ion)

Now, Na⁺ + Cl^- -> NaCl