Question

an atomic anion with a charge of $-1$ has the following electron configuration:
$kr 5s^24d^{10}5p^6$
what is the chemical symbol for the ion?
how many electrons does the ion have?
how many $4d$ electrons are in the ion?

Explanation:

Step1: Find Kr's electron count

Krypton (Kr) has 36 electrons.

Step2: Add valence electrons

Add electrons from $5s^2$, $4d^{10}$, $5p^6$: $36 + 2 + 10 + 6 = 54$

Step3: Identify neutral atom

The ion has a -1 charge, so neutral atom has $54 - 1 = 53$ electrons (iodine, I). Thus the ion is $\text{I}^-$.

Step4: Count 4d electrons

From configuration, $4d^{10}$ means 10 electrons.

Answer:

1. $\text{I}^-$
2. 54
3. 10