In peas yellow seed color y is dominant to green seed color y ​

so? what is the question in here? BTW dominant one is capital.

This detail provides the main idea that fossil fuels are rich in carbon and hydrogen.

Explanation:

As seen in the question above, fossil fuels are mainly formed from hydrocarbons. Hydrocarbons, in turn, are organic compounds, widely studied because of their wide use, composed exclusively of carbon and hydrogen atoms.

For this reason, when someone claims that "Fossil fuels are composed mostly of hydrocarbons" we can consider the main idea that fossil fuels have a large amount of carbon and hydrogen in their composition, which explains the ability to combust that these fuels have.