Question

this element is used in concrete and is the most abundant element found in the earths rocks. argon calcium silicon iron

Explanation:

Silicon is a key component in cement (a major part of concrete) and is the second - most abundant element in the Earth's crust after oxygen and very common in rocks. Argon is a noble gas and not relevant here. Calcium is important in some minerals in rocks but not the most abundant. Iron is present in rocks but not the most abundant.

Answer:

C. silicon