4.
How does a positive ion form?

Metal atoms lose electrons from their outer shell when they form ions: the ions formed are positive, because they have more protons than electrons.

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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10 years is the answer