Answer: d. All the above
Fertilizers can be deterimental to the environment. Excess use of fertilizers will result in eutrophication in the water body. Water body being more enriched with nutrients will result in excessive growth of aquatic plants. This also result in algal bloom in which algae grows on the surface of water body because of this atmospheric oxygen not able to reach the aquatic plants, hence results in oxygen depletion.
I'd say agriculture, though in more recent years you could argue for mining.
Some common elements that are gaseous state at room temperature are:
Oxygen
Nitorgen
Fluorine
Chlorine
Hydrogen
Helium
In addition, all of the elements in group VIII are gases too, they have an octet of electrons (complete outer electron shell) , they're really stable and therefore they're called noble gases. Some examples from group VIII include helium, krypton, xenon etc.
Substance exist as gases in room temperature is due to their boiling point, where is it lower than the room temperature (usually around 25°C). If their boiling point is higher than room temperature, they should exist as either solid or liquid, which is how the majority of the elements in the periodic table is.
