On fusion of a mixture of `Na_2CO_3` and ` CaCO_3` with silica at `1500^@C`, a liquid consisting of silicates of sodium and calcium is formed. On cooling . Liquid become viscous and eventually ceases to flow . It becomes solid and is known as glass. By varying the proportions of the three basic ingredients and by adding other substances, the properties of glass can be altered, Glass can be represented as `R_2 O. MO.6SiO_2`, where `R= Na` or `K, M = CaBa, Zn` or `PbSiO_2` may be replaced by `Al_2 O_3 , B_2 O_3` or `P_2 O_5`. Coloured glasses are obtained by adding certain metallic oxides or salts in the fused mass, Glass is attached by `HF` and this property is used to make marking on the glass , This is known as etching . The glass on rapid cooling becomes brittle and fragile . The articles of glass are cooled neither slowly nor very rapidly . The process of gradual cooling of glass is called annealing .
Ordinary glass is .

Options

A. Sodium silicate and silica
B. Calcium silicate and silica
C. Potassium silicate and silica
D. Mixture of sodium and calcium silicates with silica

Answer

To solve the question about ordinary glass and its composition, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Fusion Process**:
- When a mixture of sodium carbonate (`Na2CO3`), calcium carbonate (`CaCO3`), and silica (`SiO2`) is heated to `1500°C`, a liquid is formed. This liquid consists of silicates of sodium and calcium.

2. **Cooling of the Liquid**:
- Upon cooling, this liquid becomes viscous and eventually solidifies to form glass. This process indicates that the glass is a solid formed from a liquid state.

3. **Composition of Glass**:
- The general formula for glass can be represented as `R2O·MO·6SiO2`, where:
- `R` can be sodium (Na) or potassium (K).
- `M` can be calcium (Ca), barium (Ba), zinc (Zn), or lead (Pb).
- `SiO2` is the silica component.

4. **Variability in Glass Properties**:
- By varying the proportions of the ingredients and adding other substances, the properties of glass can be altered. This includes the addition of metallic oxides or salts to create colored glasses.

5. **Etching and Cooling**:
- Glass can be etched using hydrofluoric acid (HF), which allows for markings on the glass surface. The cooling process of glass is crucial; if cooled too rapidly, it becomes brittle and fragile. Therefore, a gradual cooling process known as annealing is employed.

6. **Identifying Ordinary Glass Composition**:
- The question asks about the composition of ordinary glass. Based on the fusion of sodium carbonate, calcium carbonate, and silica, we can conclude that ordinary glass consists of:
- A mixture of sodium silicate and calcium silicate along with silica.

7. **Evaluating the Options**:
- The options provided are:
- A) Sodium silicate and silica (missing calcium)
- B) Calcium silicate and silica (missing sodium)
- C) Potassium silicate and silica (missing calcium)
- D) A mixture of sodium and calcium silicates along with silica (correct answer)
- The correct answer is option D, as it includes both sodium and calcium silicates along with silica.

### Final Answer:
Ordinary glass is a mixture of sodium and calcium silicates along with silica.

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