Among the following,the $\pi$-acid ligand is

What is meant by the chelate effect? Give an example.

Which of the following cations will form the most stable complex with the same ligand?

Select the correct statement regarding the $[Ni(DMG)_2]$ complex compound.

Given below are two statements: one is labelled as "Assertion $A$" and the other is labelled as "Reason $R$".
Assertion $A$: In the complexes $Ni(CO)_4$ and $Fe(CO)_5$,the metals have zero oxidation state.
Reason $R$: Low oxidation states are found when a complex has ligands capable of $\pi$-donor character in addition to the $\sigma$-bonding.
In the light of the above statements,choose the most appropriate answer from the options given below.

Which of the following is a strong field ligand?