Conversation so far:
what are the 2 most abundant elements in the earth's crust
Oxygen and Silicon are the most abundant elements in the earth's crust
how much of the earth's crust is oxygen
Oxygen makes up 46.6% of the Earth's crust.
how much of the earth's crust is silicon
27.7% of the earth's crust is silicon
what's the third most abundant in the earths crust
Aluminum is the third most abundant element in the earth's crust

Question: what's the atomic number
Self-contained rewrite: what's the atomic number of aluminum