Which one of the following elements is least reactive with water

Options

A. Lithium
B. Sodium
C. Potassium
D. Cesium

Explanation

To determine which element is least reactive with water among the given options, we can follow these steps:

### Step 1: Identify the Elements
First, we need to identify the elements provided in the question. Typically, the elements in question would be alkali metals or alkaline earth metals, as these are known for their reactivity with water.

### Step 2: Understand Reactivity Trends
Next, we should understand the reactivity trends of these metals with water. Alkali metals (Group 1) are known to react vigorously with water, while alkaline earth metals (Group 2) react less vigorously. Among the alkali metals, the reactivity increases down the group.

### Step 3: Compare the Elements
If we consider lithium (Li), sodium (Na), potassium (K), and possibly other metals, we note that:
- Lithium reacts with water but at a slower rate compared to sodium and potassium.
- Sodium and potassium react more vigorously with water, producing hydroxides and hydrogen gas.

### Step 4: Analyze Lithium’s Reactivity
Lithium, being the first element in the alkali metal group, has a higher ionization energy compared to sodium and potassium. This means it is less willing to lose its electron and thus is less reactive with water.

### Step 5: Conclusion
Based on the above analysis, we conclude that lithium is the least reactive element with water among the alkali metals.

### Final Answer
Therefore, the element that is least reactive with water is **Lithium (Li)**.

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