Which has the least mass? (The GED Science Test)

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The GED Science Test GED - SAT

3. Which has the least mass? 

 (A) Proton 

 (B) Neutron 

 (C) Electron 

 (D) Hydrogen atom

เฉลย

3. (C) 

 An electron has nearly no discernible mass. A proton has a mass of 1 atomic mass unit (AMU) as does a neutron. According to the Periodic Table of Elements an atom of hydro- gen has a mass on average of 1AMU (1.007) since the most common isotope of hydrogen has no neutrons and is a single proton.