Question

if we have many substances then how can we find that these substence are radioactive substance

Answer 1

Radiation might sound like something dangerous, but that depends on what kind of radiation you're talking about. There are a lot of different types of radiation: the light coming from a household lamp is a type of radiation, and the microwaves that cook your food are radiation. But when we talk about radioactive substances, we're concerned with particular types of radiation.