Hydroponics has been shown to be a successful technique for growing plants. Yet,most crops are still grown on land. Why?

The technique of growing plants without soil in nutrient solutions is called:

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?

Who demonstrated the concept of hydroponics for the first time?

Hydroponics is a

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