A proton has over a _____ times the mass of an electron.

A proton has over a _____ times the mass of an electron.

• A. Hundred
• B. Thousand
• C. Ten thousand
• D. One

Answer: (B)

Comparing the rest masses of subatomic particles shows why this fits the blank. The proton’s mass is about 938 MeV/c^2, while the electron’s is about 0.511 MeV/c^2, giving a ratio of roughly 1836. That means the proton is over a thousand times heavier, but not as large as ten thousand times heavier. So the word to fill the blank is thousand. The other options don’t fit because they imply too small (hundred), too large (ten thousand), or equal masses (one).

Comparing the rest masses of subatomic particles shows why this fits the blank. The proton’s mass is about 938 MeV/c^2, while the electron’s is about 0.511 MeV/c^2, giving a ratio of roughly 1836. That means the proton is over a thousand times heavier, but not as large as ten thousand times heavier. So the word to fill the blank is thousand. The other options don’t fit because they imply too small (hundred), too large (ten thousand), or equal masses (one).