While producing hydroponic plants,which of the following metals is added along with $EDTA$?

Carefully observe the following figure.
$(a)$ Name the technique shown in the figure and the scientist who demonstrated this technique for the first time.
$(b)$ Name at least three plants for which this technique can be employed for their commercial production.
$(c)$ What is the significance of the aerating tube and feeding funnel in this setup?

$A$: Jar for nutrient solution culture contains a split cover with holes which hold a bent tube for aeration.
$R$: Regular aeration of culture solution is necessary for proper growth and activities of roots.

Why is purification of water and nutrient salts so important in studies involving mineral nutrition using hydroponics?

Who demonstrated the concept of hydroponics for the first time?

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