. Identify molecules of elements;
O2, NH3, He

Elements can be made of one atom, like He, or be elemental molecules, such as hydrogen (H2), oxygen (O2), chlorine (Cl2), ozone (O3), and sulfur (S8). Atoms are not drawn to scale. Some elements are monatomic, meaning they are made of a single (mon-) atom (-atomic) in their molecular form...

b) mutualism

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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.