What gases contribute the most to increasing the greenhouse effect? what gases are the most effective greenhouse gases? are these the same? why or why not?

The gases that contribute the most to increasing the greenhouse effect are (in order of abundance) carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and fluorinated gases (hydrofluorocarbons, perfluorocarbons, sulfur hexafluoride, and nitrogen trifluoride).

Not all of these gases are equally effective. Some are more effective than other at making the planet warmer. This "effectiveness" is measured as the Global Warming Potential (GWP). This is calculated based on how long a gas remains in the atmosphere and how strongly it absorbs energy, when compared to CO2 (GWP of 1). For example, methane has a GWP of 28-36, Nitrous Oxide has a GWP of 265-298, while chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs), hydrochlorofluorocarbons (HCFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6) have a GWP in the thousands or tens of thousands..)

a and b because with the other three, they simplify to something else.