Question:medium
Identify the incorrect statement from the following
Identify the incorrect statement from the following
Updated On: May 1, 2026
- Alkali metals react with water to form their hydroxides
- The oxidation number of K in KO2 is +4.
- Ionisation enthalpy of alkali metals decreases from top to bottom in the group.
- Lithium is the strongest reducing agent among the alkali metals.
Show Solution
The Correct Option is B
Solution and Explanation
Step 1: Understanding the Concept:
This question tests fundamental properties of alkali metals (Group 1 elements), including their reactivity, oxidation states, and periodic trends.
Step 2: Detailed Explanation:
Let's analyze each statement:
1. Statement (1): Alkali metals (M) react vigorously with water to produce metal hydroxides (MOH) and hydrogen gas.
\(2M + 2H_2O \rightarrow 2MOH + H_2\). Correct.
2. Statement (2): \(KO_2\) is potassium superoxide. In all its stable compounds, alkali metals exhibit a constant oxidation state of +1. In \(KO_2\), the superoxide ion is \((O_2)^-\), meaning the average oxidation state of oxygen is \(-1/2\), while K is +1.
Therefore, stating K is +4 is Incorrect.
3. Statement (3): Moving down the group, atomic size increases and shielding increases. The valence electron becomes further from the nucleus and is easier to remove. Thus, ionisation enthalpy decreases. Correct.
4. Statement (4): Although Lithium has the highest ionisation enthalpy in the group, it has the highest hydration enthalpy due to its small size. In aqueous solutions, this makes it the most negative \(E^\circ\) value and the strongest reducing agent. Correct.
Step 3: Final Answer:
Statement (2) is incorrect.
This question tests fundamental properties of alkali metals (Group 1 elements), including their reactivity, oxidation states, and periodic trends.
Step 2: Detailed Explanation:
Let's analyze each statement:
1. Statement (1): Alkali metals (M) react vigorously with water to produce metal hydroxides (MOH) and hydrogen gas.
\(2M + 2H_2O \rightarrow 2MOH + H_2\). Correct.
2. Statement (2): \(KO_2\) is potassium superoxide. In all its stable compounds, alkali metals exhibit a constant oxidation state of +1. In \(KO_2\), the superoxide ion is \((O_2)^-\), meaning the average oxidation state of oxygen is \(-1/2\), while K is +1.
Therefore, stating K is +4 is Incorrect.
3. Statement (3): Moving down the group, atomic size increases and shielding increases. The valence electron becomes further from the nucleus and is easier to remove. Thus, ionisation enthalpy decreases. Correct.
4. Statement (4): Although Lithium has the highest ionisation enthalpy in the group, it has the highest hydration enthalpy due to its small size. In aqueous solutions, this makes it the most negative \(E^\circ\) value and the strongest reducing agent. Correct.
Step 3: Final Answer:
Statement (2) is incorrect.
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