Food is a major problem because fertile land is decreasing as it is being used for other purposes, soil nutrients are getting depleted, and chemical fertilisers are spoiling the soil quality.
For 1 mark, one clear sentence covering the key points is enough. Examiners look for: (1) loss of fertile land, (2) soil nutrient depletion, and (3) damage due to chemical fertilisers. All three are directly from the "Problems Related to Sustainable Development" section. Avoid writing more than one to two lines.