The metal oxide used to make emerald green glass is :
- AMnO₂
- BCr₂O₇ (printed as in the paper; chromium oxide)Correct
- CCobalt oxide
- DIron oxide
Solution
Concept
Colouring oxides in glass
Step-by-step solution
1. Chromium oxide gives an emerald (bright) green colour to glass. 2. MnO₂ gives violet or acts as decolouriser, cobalt gives blue, iron gives bottle green or brown.
Explanation
Different metal oxides added to the molten glass give different colours. Chromium oxide gives emerald green; iron oxide gives a duller bottle green.
Why the other options are wrong
Manganese dioxide gives purple/violet tint, cobalt oxide gives blue, and iron oxide gives a bluish-green to brown (bottle) colour.
Shortcut
Cr = green, Co = blue, Mn = violet, Cu = turquoise/ruby red, Fe = bottle green.
Common mistake
Choosing iron oxide (bottle green).
Correct answer: B) Cr₂O₇ (printed as in the paper; chromium oxide)