What is a possible effect of a radioactive substance? it can be harmful to a person’s health. it can remove dangerous germs from food. it may electricity travel long distances. it may make some plants grow more quickly.

It is of course the first one that's correct...

    It can be harmful to a person’s health.

Explanation:   Radioactive substances are unstable particles, and the result of their half-life is radiation dangerous to human health and life. Exposure to a large amount of radiation of these particles can cause hair loss, bleeding, destruction of internal organs, damage to the central nervous system, and death. Of course, small doses of this radiation are not dangerous to human health.

Radioactive substances can also be used to remove dangerous germs from food, by killing harmful bacteria. However, this method affects the quality of food, the amount of nutrients, and it is ineffective against the virus.

Radioactive substances do not have the ability to travel through materials or even through air, other than gamma particles. Alpha and beta particles are absorbed by material and air through which they travel after only a few centimeters. The gamma particles can go a long distance, but as these are very damaging radiation of these particles, it is not advisable to use them for these purposes because the electricity in everyday use.