Which one of the following is an example of natural chelate

Among the following options, Citric acid is an example of a natural chelate.
The natural chelates are very small molecules and consequently pass through the plant's barriers including the cuticle, cell walls and cell membranes maximizing absorption and assimilation.
Citric acid had typically been used to control free iron cations in spent HCl solutions by chelating to iron and preventing the precipitation of iron hydroxide or iron sulphide.