Question

which orbital diagram represents an atom in group 18?
1s ↑↓ 2s ↑
1s ↑↓ 2s ↑↓ 2p ↑ ↑
1s ↑↓ 2s ↑↓ 2p ↑↓ ↑↓ ↑↓
1s ↑↓ 2s ↑↓

Explanation:

Step1: Recall group 18 elements' electron - configuration

Group 18 elements are noble gases with full - valence shells. The first noble gas is helium with an electron - configuration of $1s^2$. For the second period noble gas neon, the electron - configuration is $1s^22s^22p^6$.

Step2: Analyze each option

The first option has an incomplete $2s$ orbital. The second option has an incomplete $2p$ orbital. The fourth option only shows the $1s$ and $2s$ orbitals and is not a complete representation for a second - period noble gas. The third option has a full $1s$ orbital ($1s^2$), a full $2s$ orbital ($2s^2$), and a full $2p$ orbital ($2p^6$) which is consistent with the electron - configuration of a second - period noble gas.

Answer:

The third option (the one with $1s$ $\uparrow\downarrow$ $2s$ $\uparrow\downarrow$ $2p$ $\uparrow\downarrow$ $\uparrow\downarrow$ $\uparrow\downarrow$)