Question

Identify the correct statements from the following
I. LiF is less soluble in water than NaF
II. Both LiCl and MgCl\(_2\) are insoluble in ethanol
III. Both Li and Mg form nitrides
IV. Na\(_2\)CO\(_3\) gives CO\(_2\) on heating

• A. I & IV
• B. I & III
• C. I & II
• D. II & III

Hint:

The diagonal relationship between Lithium (Group 1, Period 2) and Magnesium (Group 2, Period 3) is a key concept. They share many similar properties, such as forming nitrides, having covalent halides soluble in organic solvents, and having carbonates that decompose on heating.

Answer 1

The Correct Option is B

To solve the given problem, we will evaluate each statement one by one:

1.  Statement I: "LiF is less soluble in water than NaF"
   • Lithium fluoride (LiF) is indeed less soluble in water compared to sodium fluoride (NaF). This is because LiF has a higher lattice energy due to the small size of the Li⁺ ion, which makes the compound less soluble in water. Conversely, NaF has a lower lattice energy, making it more soluble. Therefore, this statement is correct.
2. Statement II: "Both LiCl and MgCl\(_2\) are insoluble in ethanol"
   • LiCl is soluble in both water and ethanol. MgCl₂, however, is also more soluble in water. In ethanol, solubility trends can vary, but typically these salts are more soluble in polar solvents like water. Hence, the claim that both are insoluble in ethanol is not completely accurate, making this statement incorrect.
3. Statement III: "Both Li and Mg form nitrides"
   • This statement is correct. Lithium forms lithium nitride (Li₃N) and magnesium forms magnesium nitride (Mg₃N₂) upon reacting with nitrogen. Both metals can form nitrides under suitable conditions, making this statement correct.
4. Statement IV: "Na\(_2\)CO\(_3\) gives CO\(_2\) on heating"
   • Upon heating, sodium carbonate (Na₂CO₃) does not decompose readily to give carbon dioxide (CO₂). Instead, it is relatively stable to heat. However, if it were sodium bicarbonate (NaHCO₃), heating would release CO₂. Therefore, this statement is incorrect.

Based on the above evaluation, statements I and III are correct. Thus, the correct answer is I & III.