The density of `H_(2)SO_(4) …………………………..` in lead storage cell during discharging and calomel electrode is a `………………..` electrode.

Explanation

To solve the question, we need to fill in the blanks with the appropriate terms related to the lead storage cell and the calomel electrode.

### Step-by-Step Solution:

1. **Understanding the Lead Storage Cell:**
- In a lead storage cell, sulfuric acid (H₂SO₄) acts as the electrolyte. During the discharging process, the chemical reactions consume H₂SO₄, leading to a change in its concentration.

2. **Density of H₂SO₄ During Discharging:**
- As H₂SO₄ is consumed during the discharging of the lead storage cell, the concentration of the solution decreases. Since density is related to concentration, the density of H₂SO₄ will also decrease during this process.
- Therefore, we fill in the first blank with "decreases."

3. **Understanding the Calomel Electrode:**
- The calomel electrode consists of mercury(I) chloride (Hg₂Cl₂) and is commonly used as a reference electrode in electrochemical measurements.
- It is classified as a secondary reference electrode, which means it is more stable and reliable compared to the standard hydrogen electrode (SHE).

4. **Filling the Second Blank:**
- Since the calomel electrode is a secondary reference electrode, we fill in the second blank with "secondary reference."

### Final Answer:
- The density of H₂SO₄ **decreases** in the lead storage cell during discharging, and the calomel electrode is a **secondary reference** electrode.