Point source pollution:
Point source pollution is an single source of pollution that is identifiable.
So this source can be different for different pollution that is air, water, land and noise.
Non-point source pollution:
Non-point source pollution is a pollution that results from many sources.
In the given lists of pollution only option A founds to be point source of pollution, that is dumping acid from a bucket into a lake. There is a defined single source of pollution that is acid in the bucket so it is an example of point source of pollution.