What are vitamins? Which vitamin deficiency causes rickets?

Answer

### Step-by-Step Solution:

1. **Definition of Vitamins**:
- Vitamins are organic compounds that are essential for various cellular functions in the body. They are required in trace amounts.

2. **Source of Vitamins**:
- The human body cannot synthesize vitamins on its own, which means they must be obtained through diet.

3. **Classification of Vitamins**:
- Vitamins can be classified based on their solubility:
- **Fat-Soluble Vitamins**: These include Vitamin A, Vitamin D, Vitamin E, and Vitamin K.
- **Water-Soluble Vitamins**: These include Vitamin B complex (such as Thiamine (B1), Niacin (B3), Riboflavin (B2), Biotin (H), Pyridoxine (B6), Pantothenic Acid, Cobalamin (B12), Folic Acid) and Ascorbic Acid (Vitamin C).

4. **Consequences of Vitamin Deficiency**:
- A deficiency in any vitamin can lead to various diseases.

5. **Vitamin Deficiency Causing Rickets**:
- Rickets is specifically caused by a deficiency of Vitamin D. This condition leads to the softening and weakening of bones in children.

### Final Answer:
Vitamins are organic compounds required by the body in trace amounts for various cellular functions. Rickets is caused by the deficiency of Vitamin D.