Single correct option
An atom has 17 protons and 18 neutrons. After gaining one electron, the mass number and charge of the resulting ion are respectively
- A. 35 and -1
- B. 34 and -1
- C. 35 and +1
- D. 36 and 0
Show answer and solution
Answer: (A) 35 and -1
Mass number = protons + neutrons = 17 + 18 = 35, and it is not changed by gaining an electron since electrons contribute almost no mass. The extra electron gives 18 electrons against 17 protons, so the ion carries a charge of -1 (chloride ion). The options with +1 or 0 ignore the added electron.
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