Which of the following metals is most commonly used I photochemical cells?

Options

A. Lithium
B. Calcium
C. Caesium
D. Francium

Answer

To determine which metal is most commonly used in photochemical cells from the given options (lithium, calcium, cesium, and francium), we can follow these steps:

### Step 1: Understand the requirements for metals used in photochemical cells
Photochemical cells require metals that have low ionization enthalpies, which means they can easily emit electrons when exposed to light. This property is crucial for converting light energy into electrical energy.

**Hint:** Look for metals that can easily lose electrons.

### Step 2: Analyze the given options
1. **Lithium (Li)** - While lithium is an alkali metal, it has a relatively higher ionization energy compared to the others listed.
2. **Calcium (Ca)** - Calcium is an alkaline earth metal and does not fit the typical profile for photochemical applications as well as alkali metals.
3. **Cesium (Cs)** - Cesium is an alkali metal with one of the lowest ionization energies, making it very effective at emitting electrons.
4. **Francium (Fr)** - Francium is highly radioactive and unstable, making it impractical for use in photochemical cells.

**Hint:** Compare the ionization energies of the metals to see which one is the lowest.

### Step 3: Identify the most suitable metal
Among the options, cesium stands out due to its low ionization energy, which allows it to easily emit electrons when exposed to light. This characteristic makes cesium the most suitable metal for use in photochemical cells.

**Hint:** Consider the practical applications of each metal in energy conversion.

### Step 4: Conclusion
Based on the analysis, the metal that is most commonly used in photochemical cells is **cesium**.

**Final Answer:** Cesium (Option 3) is the correct choice.

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