Question

What atom is a noble gas in group 18, row 4?

Answer 1

I think you meant element?
Then it is Krypton because it is in period 4 in group 18, the noble gases.

Answer 2

Step-by-step explanation:

Group 18 is also known as noble gases. Elements of this group are helium, neon, argon, krypton, xenon, and radon.

Period 1 means value of n = 1. Period 2 means value of n = 2. Period 3 means value of n = 3. Period 4 means value of n = 4 and so on, where n is valence shell.

Electronic configuration of helium is
`1s^(2)`.

Electronic configuration of neon is
`1s^(2)2s^(2)2p^(6)`.

Electronic configuration of argon is
`1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)`.

Electronic configuration of krypton is
`1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)3d^(10)4s^(2)4p^(6)`.

Electronic configuration of xenon is
`1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)3d^(10)4s^(2)4p^(6)4d^(10)5s^(2)5p^(6)`.

Electronic configuration of radon is
`1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)3d^(10)4s^(2)4p^(6)4d^(10)5s^(2)5p^(6)4f^(14)5d^(10)6s^(2)6p^(6)`.

Therefore, we can conclude that krypton is the atom which is a noble gas in group 18, row 4.