The melting of polar ice is one effect of

The melting of polar ice is one effect of the greenhouse effect, or also global warming.

The greenhouse effect, as defined by Merriam-Webster, is "the warming of the surface and lower atmosphere of a planet (as Earth or Venus) that is caused by conversion of solar radiation into heat in a process involving selective transmission of short wave solar radiation by the atmosphere, its absorption by the planet's surface, and reradiation as infrared which is absorbed and partly reradiated back to the surface by atmospheric gases".

In short, "the warming of the surface and lower atmosphere of a planet".

The answer is b.the gaseous state is electrically positive, while the plasma state is electrically negative.