Question

What is acid rain and how does it affect the environment?

Answer 1

Acid rain affects the environment in several ways:

It can leach nutrients from the soil making then unavailable to plant life.
It an affect the growth of plants as many plants have a specific soil pH for optimum growth
Acid precipitation can change the ionic balance in clayey soils affecting their structure.
In some soils acid precipitation may free up metals (e.g. lead) in the soil that can be taken up by the plants and contaminate the associated seeds or fruit.
It can affect fish and amphibians by reducing the pH of the water impacting their health and breeding success

Answer 2

What Zhang Yan mentioned are the negative effects of acid rain. In general, I would define it as:
The poisonous gases in the air like N02, CO2, SO2 etc. mix with the rain water when it rains and reacts to form various acids. This is called acid rain.