Which of the following statements are correct ?
(i) When an animal hide, which has negatively charged particles , is soaked in tannin, which contains positively charged colloidal particles, mutual coagulation does not take place.
(ii) Photographic films are prepared by coating an emulsion of the light sensitive silver bromide in gelatin over glass plates or celluloid films.
(iii) Latex is a colloidal solution of rubber particles which are negatively charged.
(iv) In Cottrell precipitator , the smoke , before it comes out from the chimney, is led through a chamber containing plates having a charge opposite to that carried by smoke particles. The particles on coming in contact with these plates acquire some charge and do not get precipitated .

Options

A. (i) and (iv) only
B. (ii) and (iii) only
C. (ii), (iii) and (iv) only
D. All of these.

Answer

To determine which of the statements are correct, let's analyze each one step by step.

### Step 1: Analyze Statement (i)
**Statement:** When an animal hide, which has negatively charged particles, is soaked in tannin, which contains positively charged colloidal particles, mutual coagulation does not take place.

**Analysis:**
- Animal hides are typically negatively charged due to the presence of proteins.
- Tannin contains positively charged colloidal particles.
- When a negatively charged substance (animal hide) interacts with a positively charged substance (tannin), mutual coagulation occurs due to the attraction between opposite charges.

**Conclusion:** This statement is **incorrect**.

### Step 2: Analyze Statement (ii)
**Statement:** Photographic films are prepared by coating an emulsion of the light-sensitive silver bromide in gelatin over glass plates or celluloid films.

**Analysis:**
- Photographic films do indeed use an emulsion of silver bromide, which is light-sensitive, suspended in gelatin.
- This emulsion is coated onto glass plates or celluloid films to create photographic films.

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

### Step 3: Analyze Statement (iii)
**Statement:** Latex is a colloidal solution of rubber particles which are negatively charged.

**Analysis:**
- Latex is a colloidal suspension of rubber particles in water.
- The rubber particles in latex are typically negatively charged.

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

### Step 4: Analyze Statement (iv)
**Statement:** In Cottrell precipitator, the smoke, before it comes out from the chimney, is led through a chamber containing plates having a charge opposite to that carried by smoke particles. The particles on coming in contact with these plates acquire some charge and do not get precipitated.

**Analysis:**
- In a Cottrell precipitator, smoke particles (which are typically negatively charged) pass through a chamber with positively charged plates.
- When smoke particles come into contact with these plates, they lose their charge and get precipitated, settling out of the smoke.

**Conclusion:** This statement is **incorrect**.

### Final Conclusion:
- **Correct Statements:** (ii) and (iii).
- **Incorrect Statements:** (i) and (iv).

### Summary of Correct Statements:
- (ii) Photographic films are prepared by coating an emulsion of the light-sensitive silver bromide in gelatin over glass plates or celluloid films.
- (iii) Latex is a colloidal solution of rubber particles which are negatively charged.

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