Which area of Mexico is almost entirely at sea land?

Yuacatan Peninsula?

What is The name given given to the mountain range that covers most of mexico
Sierra Madre Occidental

I'm not sure I understand your first question. What about the Baja Peninsula?

I think it would be more accurate to say that this mountain range is called the Sierra Madre. Note that the Sierra Madre Oriental parallels Sierra Madre Occidental in the eastern part of the country.

1. Which area of Mexico is almost entirely at sea level?

The Yucatan Peninsula is not entirely at sea level. However, it is a low-lying area with much of its surface being limestone, resulting in the formation of extensive underground rivers and cenotes. Yucatan Peninsula is mostly known for popular tourist destinations like Cancun, Tulum, and Mayan ruins.

2. What is the name given to the mountain range that covers most of Mexico?
The mountain range that covers most of Mexico is called the Sierra Madre Occidental. It is a major mountain system that runs parallel to the western coast of Mexico, extending from the United States-Mexico border down to the southern state of Jalisco. The Sierra Madre Occidental is known for its rugged terrain, deep canyons, and diverse ecosystems. It is an important geographical feature of Mexico and has significant impacts on the climate, flora, and fauna of the region.