The Earth`s crust is composed of many elements and minerals. The four options presented are Silicon, Oxygen, Carbon, and Calcium.

1. Silicon: Although it is an abundant element, making up approximately 27.7% of the Earth`s crust by mass, it is not the most abundant.

2. Oxygen: This is the correct answer. Oxygen makes up about 46.6% of the Earth`s crust by mass, making it the most abundant element.

3. Carbon: Carbon is a relatively minor component of the Earth’s crust, contributing far less than oxygen and silicon. It forms many important compounds on the Earth, but its mass percentage is comparatively small.

4. Calcium: Calcium, although an important element in the Earth`s crust and in our bodies, is not as abundant as oxygen. It accounts for roughly 3.6% of the Earth`s crust by mass.

In conclusion, although Silicon, Carbon, and Calcium are important and abundant elements, Oxygen is found in the largest amount in terms of per cent by mass in the Earth’s crust.