Metal Oxide for Emerald Green Glass

Different metal oxides act as colorants when added to molten glass. The resulting color depends on the specific oxide used and its oxidation state within the glass matrix.

Analyzing Glass Colorants

• Option 1: $MnO_2$ (Manganese dioxide): This oxide typically imparts purple or brown hues to glass.
• Option 2: $Cr_2O_7$: This refers to chromium compounds. Chromium compounds, particularly chromium(III) oxide ($Cr_2O_3$), are widely recognized for producing green colors, often a vibrant emerald green, in glass.
• Option 3: Cobalt oxide: This results in a deep blue color, famously used in cobalt blue glass.
• Option 4: Iron oxide: Depending on the oxidation state ($Fe^{2+}$ or $Fe^{3+}$) and glass conditions, iron oxides can cause green, yellow, brown, or even blue/grey colors, but are not the primary choice for pure emerald green.

Identifying the Emerald Green Colorant

For the specific characteristic emerald green color, chromium compounds are the standard choice in glassmaking. Therefore, the option related to chromium is the correct answer.