Hydroponics is the growth of plants in

Growing plants in a nutrient solution,known as hydroponics:

What is a hydroponic solution?

Hydroponics is a system of growing plants in

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?

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