ANS:C - Potassic fertiliser

The fertiliser required for the development of fibrous materials of the plants and the sugar of vegetables & fruits is potassic fertiliser. Explanation:

1. Potassium Role in Plants: Potassium (K) is an essential nutrient for plants and plays a crucial role in various physiological processes. One of its key functions is promoting overall plant vigor and health, including the development of strong, fibrous materials such as stems and roots.
2. Sugar Content in Fruits and Vegetables: Potassium also influences the accumulation of sugars in fruits and vegetables. Adequate potassium levels in the soil contribute to improved sugar content, flavor, and overall quality of harvested produce.
3. Fruit and Vegetable Quality: Potassium helps regulate various metabolic processes related to sugar metabolism, enzyme activation, and water balance in plants. As a result, it directly affects the synthesis and accumulation of sugars in fruits and vegetables, enhancing their sweetness, texture, and nutritional value.
4. Potassic Fertilisers: Potassic fertilisers, such as potassium sulfate (K2SO4) or potassium chloride (KCl), supply potassium to plants, ensuring that they have an adequate supply of this essential nutrient for optimal growth and development.
5. Balanced Nutrition: While nitrogenous and phosphatic fertilisers are also important for plant growth, potassic fertilisers specifically address the need for potassium, which is crucial for the development of fibrous materials and the sugar content of fruits and vegetables.