Why caesium and potassium are used as electrodes in photoelectric cells ?

Explanation

### Step-by-Step Solution:

1. **Understanding the Context**:
- Caesium (Cs) and potassium (K) are both alkali metals, which belong to Group 1 of the periodic table.

2. **Properties of Alkali Metals**:
- Alkali metals are known for their large atomic sizes and low ionization energies. As we move down the group in the periodic table (from lithium to francium), the size of the atoms increases.

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