Question

which ion in the ground state has the same electron configuration as an atom of neon in the ground state?

1. $\ce{k+}$
2. $\ce{li+}$
3. $\ce{f-}$
4. $\ce{cl-}$

Explanation:

Step1: Find neon's electron count

Neon (Ne) atomic number = 10, so electron count = 10. Ground state electron configuration: $1s^22s^22p^6$.

Step2: Calculate electrons in each ion

• $K^+$: K atomic number 19, loses 1 electron: $19-1=18$ electrons
• $Li^+$: Li atomic number 3, loses 1 electron: $3-1=2$ electrons
• $F^-$: F atomic number 9, gains 1 electron: $9+1=10$ electrons
• $Cl^-$: Cl atomic number 17, gains 1 electron: $17+1=18$ electrons

Step3: Match electron count to neon

Only $F^-$ has 10 electrons, matching neon's electron configuration.

Answer:

1. $F^-$