Question

According to Lewis the ligands are:
(A) Acidic in nature
(B) Basic in nature
(C) Neither acidic nor basic
(D) Some are acidic and others are basic

Answer 1

Hint: Coordination compounds are those compounds in which the central metal atom (M) is coordinated to ions or the functional group called the ligands (L). The bond is formed in these compounds as a result of the donation of electrons from the ligands to the central metal atom. These ligands can be either Monodentate (with 1 donor site) like Nitrido $ \left( {{N^{3 - }}} \right) $ , Bidentate (with 2 donar sites) like oxalate ion $ ({C_2}{O_4}^{2 - }) $ , or Polydentate (with more than 2 donar sites) like EDTA which is a hexadentate ligand (6 donor sites).

Complete answer:
According to Lewis, Lewis acids accept the electrons, and Lewis bases are those that donate the electrons. The donation of electrons from Lewis base to acid results in the formation of a coordinate covalent bond.
Central Metal atoms are generally the d-block (or transition) elements with vacant or empty d orbitals that can readily accept electrons. Like- $ C{u^{ + 2}}\left( {{d^9}} \right),C{r^{ + 3}}\left( {{d^3}} \right),N{i^{ + 2}}\left( {{d^8}} \right) $ etc. The ligand may be neutral with lone pair of electrons like Ammonia $ \left( {N{H_3}} \right) $ or may be Anionic (atoms with a negative charge) like halides $ \left( {{X^ - }} \right) $ . Ligands are also called Complexing agents.
Let us take an example to understand it-
 $ {\left[ {Co{{\left( {N{H_3}} \right)}_6}} \right]^{2 + }} $ is a coordination complex where Copper (II) acts as a central metal atom with d9 configuration while Ammonia $ \left( {N{H_3}} \right) $ that contains lone pair acts as the ligand.
The coordination compounds are formed as a result of the Lewis acid-base reaction. The properties of the coordination complex are different from the properties of metal and ligands with which it is composed. Here the central Metal atom accepts electrons and hence acts as lewis acid while ligands act as donors of electrons hence they act as lewis base.
So Option (B) is correct.

Note:
The total number of sigma bonds formed between the central metal atom and the ligands is called the Coordination number. In most cases ligands act as lewis bases however some ligands can accept electrons from the metal, this phenomenon is called pi-back bonding. Here we name them pi-acid ligands. Examples of such ligands are $ CO, C{N^ - },P{F_3} $ etc.