Which of these situations is a direct example of water pollution?
1. runoff carries fertilizer from lawn to nearby lake.
2. a cars exhaust pipe releases emissions into the air.
3. food waste rots in a compost bin instead of in a trash can.
4. barrels collect rainwater to be used for watering flower gardens.

The first one, runoff carries fertilizer from a lawn to a nearby lake, is the most direct example of water pollution. 

The fertilizer contains chemicals that are bad for the environment, and when it rains and that water is carried down to a lake or river, that can be bad for the environment of the body of water. 

Sugar and water are chemically combined.(a solution is chemically combined while a mixture is mixed together without bonding the molecules)