Which one of the following reacts vigorously with cold water?

Options

A. Sodium
B. Carbon
C. Aluminium
D. Magnesium

Explanation

To determine which metal reacts vigorously with cold water, we can follow these steps:

### Step 1: Identify the Metals
First, we need to identify the metals that are being considered in the question. Common metals that are known to react with water include sodium (Na), potassium (K), calcium (Ca), and magnesium (Mg).

### Step 2: Understand the Reactivity of Metals
Next, we should understand the general reactivity of these metals with water. Alkali metals (such as sodium and potassium) are known for their vigorous reactions with water. They have low ionization energy (IE) and high heat of hydration (HE), which contribute to their reactivity.

### Step 3: Compare the Reactivity
Among the metals listed:
- **Sodium (Na)**: Reacts vigorously with cold water, producing sodium hydroxide and hydrogen gas.
- **Potassium (K)**: Reacts even more vigorously than sodium with cold water.
- **Calcium (Ca)**: Reacts moderately with water, but not as vigorously as sodium or potassium.
- **Magnesium (Mg)**: Reacts very slowly with cold water and requires hot water or steam for a more vigorous reaction.

### Step 4: Conclusion
Based on the reactivity of these metals with cold water, we conclude that **sodium (Na)** and **potassium (K)** react vigorously. However, potassium reacts more vigorously than sodium.

### Final Answer
The metal that reacts most vigorously with cold water is **potassium (K)**.

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