Methyl orange and phenolpthalein are common chemical indicators often used in titrations. what is the role of a chemical indicator?

Explanation:

Chemical indicators:-

They are species or the substances which are added to the reaction mixture. They undergoes a specific and distinct observable change in the reaction mixture indicating  the formation of consumption of the species in the reaction mixture. The change can be a color change, olfactory change, etc.

Example:-

Methyl yellow which imparts yellow colour to the alkaline solutions and is red in acidic solutions.

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.