The pair that yields the same gaseous product on reaction with water `:`

Options

A. K and `KO_(2)`
B. Ba and `BaO_(2)`
C. Ca and `CaH_(2)`
D. Na and `Na_(2)O_(2)`

Answer

To determine which pair of reactants yields the same gaseous product when they react with water, we will analyze each option provided.

### Step-by-Step Solution:

1. **Identify the Reactants:**
We have four pairs of reactants:
- A: K and KO2
- B: Ba and BaO2
- C: Ca and CaH2
- D: Na and Na2O2

2. **Analyze Option A (K and KO2):**
- **K + H2O → KOH + H2**
- Potassium reacts with water to produce potassium hydroxide and hydrogen gas.
- **KO2 + H2O → KOH + H2O2**
- Potassium superoxide reacts with water to produce potassium hydroxide and hydrogen peroxide.
- **Gaseous Product:** Different (H2 from K and none from KO2).

3. **Analyze Option B (Ba and BaO2):**
- **Ba + H2O → Ba(OH)2 + H2**
- Barium reacts with water to produce barium hydroxide and hydrogen gas.
- **BaO2 + H2O → Ba(OH)2 + H2O2**
- Barium peroxide reacts with water to produce barium hydroxide and hydrogen peroxide.
- **Gaseous Product:** Different (H2 from Ba and none from BaO2).

4. **Analyze Option C (Ca and CaH2):**
- **Ca + H2O → Ca(OH)2 + H2**
- Calcium reacts with water to produce calcium hydroxide and hydrogen gas.
- **CaH2 + H2O → Ca(OH)2 + H2**
- Calcium hydride reacts with water to produce calcium hydroxide and hydrogen gas.
- **Gaseous Product:** Same (H2 from both).

5. **Analyze Option D (Na and Na2O2):**
- **Na + H2O → NaOH + H2**
- Sodium reacts with water to produce sodium hydroxide and hydrogen gas.
- **Na2O2 + H2O → NaOH + H2O2**
- Sodium peroxide reacts with water to produce sodium hydroxide and hydrogen peroxide.
- **Gaseous Product:** Different (H2 from Na and none from Na2O2).

6. **Conclusion:**
The pair that yields the same gaseous product on reaction with water is **Option C: Ca and CaH2**, as both yield hydrogen gas.

### Final Answer:
**Option C: Ca and CaH2**