Alkali metals are extremely reactive because they 1. have very small atomic masses
2. are not solid at room temperature
3. have one valence electron that is easily removed to form a positive ion
4. have two valence electrons that form compounds with calcium and magnesium

i think it is (3

Explanation:

They tend to donate their electrons in reactions and have an oxidation state of +1.

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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