Here's why:

* Electronic Configuration: Carbon has an atomic number of 6, meaning it has 6 protons and 6 electrons. Its electronic configuration is 2, 4.

* Energy Levels: The first energy level (also called the K shell) can hold a maximum of 2 electrons.

* Filling Order: Electrons fill energy levels starting with the lowest energy level.

So, the first energy level of carbon is completely filled with 2 electrons.