Question

what is the electron configuration for this particle? $\text{sr}^{2+}$
$1s^22s^22p^63s^23p^64s^23d^{10}4p^65s^1$
$1s^22s^22p^63s^23p^64s^23d^{10}4p^6$
$1s^22s^22p^63s^23p^6$
$1s^22s^22p^63s^23p^64s^23d^{10}4p^65s^2$

Explanation:

Step1: Find Sr's atomic number

Strontium (Sr) has an atomic number of 38, so a neutral Sr atom has 38 electrons.

Step2: Account for +2 charge

Sr²⁺ loses 2 electrons, so total electrons = 38 - 2 = 36.

Step3: Write full electron config

Fill orbitals in Aufbau order: $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6$ (this matches 36 electrons, same as Kr, a noble gas).

Answer:

$1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6$ (the second option)