Which of statements are true?

Options

A. `NaHCO_(3) and KHCO_(3)` have same crystal structure
B. On heating `LiNO_(3)` decomposes into `Li_(2)O an CO_(2)`
C. Among alkali metals, Li metal impart red colour flame
D. `Li_(2)SO_(4)` does not form alum

Answer

To determine which statements are true regarding the s-block elements, we will analyze each statement one by one.

### Step 1: Analyze the first statement
**Statement:** NaHCO3 and KHCO3 have the same crystal structure.

- **Analysis:** Sodium bicarbonate (NaHCO3) and potassium bicarbonate (KHCO3) do not have the same crystal structure. NaHCO3 forms a polymeric structure with HCO3 ions linked by an infinite chain, while KHCO3 forms a dimeric anion. Therefore, the crystal structures differ: NaHCO3 has a face-centered cubic structure, and KHCO3 has a body-centered cubic structure.

**Conclusion:** This statement is **incorrect**.

### Step 2: Analyze the second statement
**Statement:** On heating, LiNO3 decomposes into Li2O and CO2.

- **Analysis:** When lithium nitrate (LiNO3) is heated, it decomposes to form nitrogen dioxide (NO2) and lithium oxide (Li2O), not carbon dioxide (CO2). Thus, the statement is incorrect.

**Conclusion:** This statement is **incorrect**.

### Step 3: Analyze the third statement
**Statement:** Among alkali metals, lithium metal imparts a red color flame.

- **Analysis:** Lithium does indeed impart a red color to the flame when burned. This is due to the ionization energy of lithium, which allows it to emit light at specific wavelengths.

**Conclusion:** This statement is **correct**.

### Step 4: Analyze the fourth statement
**Statement:** Li2SO4 does not form alum.

- **Analysis:** Alum is a type of double sulfate salt with the general formula AMSO4·12H2O, where A is a monovalent cation and M is a trivalent cation. Lithium (Li) is too small to fit into the crystalline structure required for alum formation, thus Li2SO4 does not form alum.

**Conclusion:** This statement is **correct**.

### Final Conclusion
Among the given statements, the true statements are:
- Statement 3: Lithium imparts a red color flame.
- Statement 4: Li2SO4 does not form alum.

### Summary of True Statements
- Statement 3 is **true**.
- Statement 4 is **true**.
- Statements 1 and 2 are **false**.