Which one of the following is present in the largest amount in terms of per cent by mass in the earth's crust?

1. The question asks about the element present in the largest amount by mass in the earth's crust. 2. The approximate composition of the Earth's crust by mass is: - Oxygen (O): ~46.6% - Silicon (Si): ~27.7% - Aluminum (Al): ~8.1% - Iron (Fe): ~5.0% - Calcium (Ca): ~3.6% - Sodium (Na): ~2.8% - Potassium (K): ~2.6% - Magnesium (Mg): ~2.1% - Others: ~1.5% 3. Carbon (C) is relatively rare in the crust itself, though abundant in the biosphere and atmosphere. 4. Clearly, Oxygen is present in the largest amount by mass.