Which of the following statements are true?

Options

A. `NaHCO_(3) and KHCO_(3)` have same crystal structure
B. On heating `LiNO_(3)` decomposes into `Li_(2)O and 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 given compounds and their properties, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement 1: NaHCO3 and KHCO3 have the same crystal structure.**
- **Analysis:** Sodium bicarbonate (NaHCO3) and potassium bicarbonate (KHCO3) both contain the bicarbonate ion (HCO3-). However, their crystal structures differ. In NaHCO3, the HCO3- ions form an infinite chain structure, while in KHCO3, the HCO3- ions form a dimeric anion structure. Therefore, this statement is **false**.

2. **Statement 2: On heating LiNO3 decomposes into Li2O and CO2.**
- **Analysis:** When lithium nitrate (LiNO3) is heated, it decomposes to form lithium oxide (Li2O), nitrogen dioxide (NO2), and oxygen (O2). The correct decomposition reaction is:
\[ 4 \text{LiNO}_3 \rightarrow 2 \text{Li}_2\text{O} + 4 \text{NO}_2 + \text{O}_2 \]
- Since the statement incorrectly mentions CO2 instead of NO2, this statement is **false**.

3. **Statement 3: Among alkali metals, lithium metal imparts red color flame.**
- **Analysis:** Alkali metals impart characteristic colors to a flame when heated. Lithium specifically imparts a crimson red color to the flame, not just red. Therefore, the statement is misleading as it does not specify the correct shade. This statement is **false**.

4. **Statement 4: Li2SO4 does not form alum.**
- **Analysis:** Alums are double sulfate salts with the general formula \( \text{AMSO}_4 \cdot 12 \text{H}_2\text{O} \), where A is a monovalent cation (like potassium or ammonium) and M is a trivalent cation (like aluminum). Due to the small size of lithium compared to potassium and ammonium, lithium cannot fit into the crystalline structure of alums. Thus, this statement is **true**.

### Conclusion:
The true statements are:
- **Statement 4**: Li2SO4 does not form alum.