Which of the following is//are false?

Options

A. `Na_(2)Cr_(2)O_(7)` is used as a primary standard in volumetric analysis.
B. Potassium permanganate in excess on treatment with conc. `H_(2)SO_(4)` form manganese heptoxide
C. phosphine, astatine all precipitates silver from silver nitrate.
D. From Kipp's apparatus waste ferric sulphate and ferrous sulphate mixture is obtained when air or oxygen is passed for longer time.

Explanation

To determine which of the statements is false, we will analyze each statement one by one.

### Step 1: Analyze Statement 1
**Statement:** Na2Cr2O7 is used as a primary standard in volumetric analysis.

**Analysis:**
- Sodium dichromate (Na2Cr2O7) is hygroscopic, meaning it absorbs moisture from the air.
- Due to its deliquescent nature, it cannot be reliably used as a primary standard because its mass can change with humidity.
- Therefore, this statement is **false**.

### Step 2: Analyze Statement 2
**Statement:** Potassium permanganate in excess on treatment with concentrated H2SO4 forms manganese heptoxide.

**Analysis:**
- The reaction of potassium permanganate (KMnO4) with concentrated sulfuric acid (H2SO4) produces manganese heptoxide (Mn2O7).
- The balanced reaction is:
\[ 2 KMnO4 + 3 H2SO4 \rightarrow Mn2O7 + K2SO4 + 3 H2O \]
- This statement is **true**.

### Step 3: Analyze Statement 3
**Statement:** Phosphine and astatine precipitate silver from silver nitrate.

**Analysis:**
- Phosphine (PH3) reacts with silver nitrate (AgNO3) to form a silver phosphide precipitate.
- The reaction can be represented as:
\[ 3 AgNO3 + PH3 \rightarrow Ag3P + 3 HNO3 \]
- Astatine (AsH3) also reacts similarly with silver nitrate.
- Therefore, this statement is **true**.

### Step 4: Analyze Statement 4
**Statement:** From the Kip's apparatus, waste ferric sulfate and ferrous sulfate are obtained when air (oxygen) is passed for a longer time.

**Analysis:**
- In the Kip's apparatus, iron pyrite (FeS2) reacts with oxygen and water to initially form ferrous sulfate (FeSO4).
- With prolonged exposure to oxygen, ferrous sulfate can oxidize to form ferric sulfate (Fe2(SO4)3).
- The reactions are:
\[ 4 FeS2 + 15 O2 + 6 H2O \rightarrow 4 FeSO4 + 4 H2SO4 \]
\[ 4 FeSO4 + O2 + 2 H2O \rightarrow 2 Fe2(SO4)3 + 2 H2SO4 \]
- Thus, this statement is **true**.

### Conclusion
After analyzing all the statements, the only false statement is:

**False Statement:** Na2Cr2O7 is used as a primary standard in volumetric analysis.

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