Which of the following metal reacts least vigorously with water?

Options

A. Li
B. Na
C. K
D. Cs

Answer

To determine which metal reacts least vigorously with water among Lithium, Sodium, Potassium, and Caesium, we can follow these steps:

### Step 1: Identify the Group of Metals
All the metals listed (Lithium, Sodium, Potassium, and Caesium) belong to Group 1 of the periodic table, known as alkali metals.

**Hint:** Group 1 metals are characterized by their reactivity with water, forming hydroxides and releasing hydrogen gas.

### Step 2: Understand the Reactivity Trend
In alkali metals, the reactivity with water increases as you move down the group. This means that as you go from Lithium to Caesium, the metals become more reactive.

**Hint:** Remember that the reactivity of alkali metals increases down the group due to the increasing atomic size and decreasing ionization energy.

### Step 3: Compare the Reactivity of Each Metal
- **Lithium**: Reacts with water but less vigorously compared to the others.
- **Sodium**: Reacts vigorously with water, producing heat and hydrogen gas.
- **Potassium**: Reacts even more vigorously than sodium, often resulting in a more explosive reaction.
- **Caesium**: Reacts extremely violently with water, often causing explosions.

**Hint:** Think about the intensity of reactions you have learned about for each metal.

### Step 4: Conclusion
Based on the reactivity trend of alkali metals, Lithium is the metal that reacts least vigorously with water.

**Final Answer:** **Lithium** reacts least vigorously with water among the given options.