Question

how carbanion are obtained​

Answer 1

These carbanions are formed when bond between carbon attached to a lesser electronegative atom breaks heterolytically. Hence carbanion is an anion in which carbon has an pair of electrons which is unshared and this excess electron is responsible for the negative charge on the carbon.

Answer 2

Carbanions are formally derived from neutral organic molecules by removal of positively charged atoms or groups of atoms.