The catalyst used for hydrogenation of vegetable oils is _____ .

Explanation

**Step-by-Step Text Solution:**

1. **Understanding Hydrogenation**: Hydrogenation is a chemical process where hydrogen is added to unsaturated vegetable oils to convert them into saturated fats. This process is important for improving the stability and shelf-life of oils.

2. **Role of Catalyst**: A catalyst is a substance that increases the rate of a chemical reaction without being consumed or permanently altered in the process. In the case of hydrogenation, a catalyst is necessary to facilitate the reaction between hydrogen and unsaturated oils.

3. **Identifying the Catalyst**: In the hydrogenation of vegetable oils, the most commonly used catalyst is nickel. Nickel helps in speeding up the reaction between molecular hydrogen and the unsaturated bonds in vegetable oils.

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