**Explanation:**

**Vitamin C** is the vitamin that is lost by heating.

**1. Heat Sensitivity of Vitamin C:**
Vitamin C, also known as ascorbic acid, is highly sensitive to heat. When foods containing vitamin C are cooked or heated, the heat can destroy or degrade the vitamin, resulting in a loss of its nutritional value. The higher the temperature and the longer the cooking time, the more vitamin C is lost.

**2. Effects of Heat on Vitamin C:**
- Oxidation: Vitamin C is easily oxidized when exposed to air, light, and heat. Oxidation breaks down the molecular structure of vitamin C, causing it to lose its nutritional benefits.
- Destruction: High temperatures can cause the breakdown of vitamin C molecules, resulting in a loss of its potency. Boiling, baking, and frying can lead to a significant reduction in vitamin C content.
- Leaching: When vegetables or fruits are cooked in water, some of the vitamin C content can be lost through leaching. The heat causes the vitamin to dissolve in the cooking water, reducing its concentration in the food.

**3. Ways to Preserve Vitamin C:**
To minimize the loss of vitamin C during cooking or heating, it is important to adopt certain methods:
- Use minimal water: When cooking vegetables or fruits, use the minimum amount of water necessary to prevent excessive leaching of vitamin C.
- Steam instead of boiling: Steaming is a gentler cooking method that helps retain more of the nutrients, including vitamin C, compared to boiling.
- Cook for a shorter duration: Reduce the cooking time to minimize exposure to heat and preserve more of the vitamin C content.
- Choose fresh produce: Fresh fruits and vegetables tend to have higher vitamin C content compared to processed or canned varieties.

In conclusion, vitamin C is the vitamin that is lost by heating. To retain the maximum nutritional value, it is advisable to consume fruits and vegetables raw or cook them using methods that minimize heat exposure.

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