In your own words, explain how a large number estimation with only one significant figure l means adding or subtracting a few should not affect the estimation?

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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i'm pretty sure its b i might be wrong though!

there is none because earth is stationary and flat.