Which of the following reacts most vigrously with water

Options

A. Ca
B. Be
C. Sr
D. Mg

Answer

To determine which of the following elements reacts most vigorously with water, we can analyze the reactivity of Group 2 elements (alkaline earth metals). The elements in question are likely to be Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), and Barium (Ba).

### Step-by-Step Solution:

1. **Identify the Group**:
- The elements in question are from Group 2 of the periodic table, which includes Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), and Barium (Ba).

**Hint**: Remember that Group 2 elements are known as alkaline earth metals.

2. **Understand Electropositivity**:
- Electropositivity refers to the ability of an element to lose electrons. As you move down the group from Be to Ba, the electropositive character increases.

**Hint**: Electropositive character increases down the group due to decreasing ionization enthalpy.

3. **Ionization Enthalpy**:
- The ionization enthalpy decreases as you move down the group. This means it becomes easier to remove the outermost electron, leading to increased reactivity.

**Hint**: Consider how atomic size affects the attraction between the nucleus and the outermost electron.

4. **Electrode Potential**:
- The standard electrode potential (E°) becomes more negative as you move down the group. For example:
- Be: E° = -1.97 V
- Mg: E° = -2.36 V
- Ca: E° = -2.76 V
- Sr: E° = -2.89 V
- Ba: E° = -2.92 V
- A more negative E° value indicates a greater tendency to lose electrons and react.

**Hint**: The more negative the electrode potential, the more vigorous the reaction with water.

5. **Reactivity with Water**:
- Beryllium does not react with water, while the reactivity increases down the group. Strontium and Barium react vigorously with water, producing hydroxides and hydrogen gas.

**Hint**: Remember that the reaction of alkaline earth metals with water produces metal hydroxides and hydrogen gas.

6. **Conclusion**:
- Among the Group 2 elements, Barium (Ba) and Strontium (Sr) react most vigorously with water. However, Strontium is known to react more vigorously than Barium due to its position in the group.

**Final Answer**: Strontium (Sr) reacts most vigorously with water.