Which of the following is correct?

Options

A. LiH is thermally more stable than CsH
B. Density of `H_(2)` is about `(1)/(14)`th of that of air
C. Atomic hydrogen is much more reactive than ordinary hydrogen
D. All of these

Answer

To solve the question "Which of the following is correct?" regarding hydrogen, we will evaluate each option one by one.

### Step 1: Evaluate Option 1
**Statement:** Lithium hydride is thermally more stable than cesium hydride.

**Analysis:**
- Lithium hydride (LiH) has a smaller cation (Li⁺) compared to cesium hydride (CsH) which has a larger cation (Cs⁺).
- The smaller size of lithium allows for a higher lattice energy due to stronger ionic bonds.
- Higher lattice energy generally indicates greater thermal stability.

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

### Step 2: Evaluate Option 2
**Statement:** The density of hydrogen is about 1/14th of that of air.

**Analysis:**
- The density of hydrogen gas (H₂) is indeed much lower than that of air.
- The density of hydrogen is approximately 0.0899 g/L, while the density of air is about 1.225 g/L.
- Therefore, the density of hydrogen is roughly 1/14th of the density of air.

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

### Step 3: Evaluate Option 3
**Statement:** Atomic hydrogen is much more reactive than ordinary hydrogen.

**Analysis:**
- There are three forms of hydrogen: atomic hydrogen (H), nascent hydrogen, and molecular hydrogen (H₂).
- Atomic hydrogen is highly reactive due to its single electron, making it more reactive than molecular hydrogen, which is stable.
- The order of reactivity is atomic hydrogen > nascent hydrogen > molecular hydrogen.

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

### Step 4: Evaluate Option 4
**Statement:** All of these.

**Analysis:**
- Since we have established that Options 1, 2, and 3 are all correct, it follows that Option 4, which states "all of these," is also correct.

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

### Final Answer
The correct option is **Option 4: All of these**.

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