Which of the following is used to remove the green colour from glass?

Manganese dioxide

The correct answer is option 2. Manganese dioxide.

Manganese dioxide \((MnO_2)\) is used to remove the green color from glass due to its oxidizing properties.

The green color observed in glass is often caused by the presence of iron impurities. During the manufacturing process of glass, small amounts of iron compounds may be introduced unintentionally. These iron impurities can impart a greenish tint to the glass, which is undesirable for certain applications where colorless or clear glass is preferred.

Manganese dioxide is a strong oxidizing agent. When added to glass batch materials during the glassmaking process, manganese dioxide reacts with iron impurities present in the glass. Specifically, manganese dioxide oxidizes the iron ions \((Fe^{2+})\) to higher oxidation states \((Fe^{3+})\), which results in the formation of colorless or pale yellow iron oxides.

By oxidizing the iron impurities, manganese dioxide effectively neutralizes the green coloration caused by these impurities. The resulting glass appears clearer and more transparent, without the unwanted green hue.

Manganese dioxide is commonly used as a decolorizing agent in the production of clear or colorless glass, such as window glass, tableware, and laboratory glassware. It helps improve the aesthetic quality of the glass by removing undesired coloration and enhancing its transparency.

Apart from its use in glassmaking, manganese dioxide has various other applications. It is employed as a catalyst in chemical reactions, a depolarizer in dry-cell batteries, and a pigment in paints and ceramics, among other uses.

In summary, manganese dioxide is used to remove the green color from glass by oxidizing iron impurities, thereby improving the clarity and transparency of the glass. Its oxidizing properties make it an effective decolorizing agent in the glassmaking industry.