Answer : 2. "aluminum"
Explanation :

Manikya, also known as ruby, and sapphire are gemstones that are forms of the mineral corundum. Corundum is not an oxide but rather a crystalline form of aluminum oxide (Al₂O₃). Both ruby and sapphire are varieties of corundum, with ruby being red due to the presence of chromium impurities, and sapphire coming in various colors, except red (which would be classified as ruby), often due to different trace elements.