What class of elements includes all of the elements that are gases at room temperature?
a. non metals
b. metals
c. metalloids

Answer is: Nonmetals - noble gases (group 18).

This question is not complete, because some nonmetals are solid (carbon, sulfur) and liquid (bromine) at room temperature.

The nonmetals are divided into two categories: reactive nonmetals and noble gases.

Noble gases are in group 18: helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and radon (Rn). They have very low chemical reactivity.

acid rain does not usually kill trees directly. instead, it is more likely to weaken the trees by damaging their leaves, limiting the nutrients available to them, or poisoning them with toxic substances slowly released from the soil. the main atmospheric pollutants that affect trees are nitrates and sulphates.