Which property of argon makes it useful for potassium-argon dating?

It decays into potassium.
It is an unstable element.
It remains trapped in rock.
It is useful only for dating newer rock.

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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the answer is b. dilution