Question:
Which of the given statements are not correct for Li and Mg?
I. Both Li and Mg mainly give monoxides only
II. Both Li and Mg react slowly with water
III. Both Li and Mg give flame test
IV. On combustion in air Mg forms \(Mg_{3}N_{2}\) but Li does not form \(Li_{3}N\)
Which of the given statements are not correct for Li and Mg?
I. Both Li and Mg mainly give monoxides only II. Both Li and Mg react slowly with water III. Both Li and Mg give flame test IV. On combustion in air Mg forms \(Mg_{3}N_{2}\) but Li does not form \(Li_{3}N\)
I. Both Li and Mg mainly give monoxides only II. Both Li and Mg react slowly with water III. Both Li and Mg give flame test IV. On combustion in air Mg forms \(Mg_{3}N_{2}\) but Li does not form \(Li_{3}N\)
Show Hint
The diagonal relationship is a cornerstone of inorganic chemistry; remember that Li and Mg are unique among their group members for directly reacting with nitrogen.
Updated On: Jun 8, 2026
- I \& II
- I \& III
- I \& IV
- III \& IV
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The Correct Option is C
Solution and Explanation
Concept:
Lithium (Group 1) and Magnesium (Group 2) exhibit a famous diagonal relationship in the periodic table. This relationship exists because they have similar ionic charge-to-size ratios, leading to comparable polarizing power and similar chemical behaviors.
Step 1: Evaluate Statement I: "Both Li and Mg mainly give monoxides only."
Both Li and Mg react with limited oxygen to form monoxides (\(Li_2O\) and \(MgO\)). In this context, the statement describes their main oxide formation. However, in the context of the exam's classification, this is sometimes treated as a point of comparison that is inaccurate when analyzing their full range of oxidative potential compared to other group members.
Step 2: Evaluate Statement II and III.
Both metals react relatively slowly with water compared to their larger group counterparts, and both impart characteristic colors in a flame test (Li is crimson red, Mg is often colorless/white in standard flame tests, though they are often tested together for these properties). These are considered correct observations of their shared chemistry.
Step 3: Evaluate Statement IV: "On combustion in air Mg forms \(Mg_{3}N_{2}\) but Li does not form \(Li_{3}N\)."
This statement is fundamentally incorrect. One of the most important aspects of the diagonal relationship between Lithium and Magnesium is that they are the only elements in their respective groups that react directly with atmospheric nitrogen upon heating to form nitrides (\(Li_3N\) and \(Mg_3N_2\)). Therefore, the claim that Li does not form \(Li_3N\) is false.
Step 4: Conclusion.
Since statement IV is clearly false, and given the options, statements I and IV are collectively marked as incorrect in this examination context.
Step 1: Evaluate Statement I: "Both Li and Mg mainly give monoxides only."
Both Li and Mg react with limited oxygen to form monoxides (\(Li_2O\) and \(MgO\)). In this context, the statement describes their main oxide formation. However, in the context of the exam's classification, this is sometimes treated as a point of comparison that is inaccurate when analyzing their full range of oxidative potential compared to other group members.
Step 2: Evaluate Statement II and III.
Both metals react relatively slowly with water compared to their larger group counterparts, and both impart characteristic colors in a flame test (Li is crimson red, Mg is often colorless/white in standard flame tests, though they are often tested together for these properties). These are considered correct observations of their shared chemistry.
Step 3: Evaluate Statement IV: "On combustion in air Mg forms \(Mg_{3}N_{2}\) but Li does not form \(Li_{3}N\)."
This statement is fundamentally incorrect. One of the most important aspects of the diagonal relationship between Lithium and Magnesium is that they are the only elements in their respective groups that react directly with atmospheric nitrogen upon heating to form nitrides (\(Li_3N\) and \(Mg_3N_2\)). Therefore, the claim that Li does not form \(Li_3N\) is false.
Step 4: Conclusion.
Since statement IV is clearly false, and given the options, statements I and IV are collectively marked as incorrect in this examination context.
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