Which source of water pollution would be the hardest to trace and control?

Nonpoint pollution is harder to control

Explanation:

Nonpoint pollution is harder to control because they include runoff from farms, golf courses, construction sites, roads. Whereas the single origin of the pollution is harder to trace.

it is to be noted that an alpha particle is an helium nucleus. so it contains 2 protons 2 neutrons and has a mass number of 4. when alpha decay particles are ejected from the nucleus it gets transformed into an atom which has atomic number less than 2 and a mass number less than 4.

an equation that could represent alpha decay is radium 226 decay of alpha particle forms radon 222.

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i believe you are right for all except the 3rd ( look at sqdancefan his answer is much better)