Question

Neutral atoms of neon (atomic number 10) have the same number of electrons as each of the following except:

Na^+
Mg^+2
F^-
Ar
0^-2

Answer 1

Answer : The correct option is, Ar

Explanation :

(1) The element is,
`Na^+`

Atomic number of Na = 11

The general electronic configuration of Na is,
`1s^22s^22p^63s^1`

The electronic configuration of
`Na^+` is,
`1s^22s^22p^6`

The number of electrons in
`Na^+` = 10

(2) The element is,
`Mg^(2+)`

Atomic number of Mg = 12

The general electronic configuration of Mg is,
`1s^22s^22p^63s^2`

The electronic configuration of
`Mg^(2+)` is,
`1s^22s^22p^6`

The number of electrons in
`Mg^(2+)` = 10

(3) The element is,
`F^-`

Atomic number of F = 9

The general electronic configuration of F is,
`1s^22s^22p^5`

The electronic configuration of
`F^-` is,
`1s^22s^22p^6`

The number of electrons in
`F^-` = 10

(4) The element is, Ar

Atomic number of Ar = 18

The general electronic configuration of Ar is,
`1s^22s^22p^63s^23p^6`

The number of electrons in Ar = 18

(5) The element is,
`O^(2-)`

Atomic number of O = 8

The general electronic configuration of O is,
`1s^22s^22p^4`

The electronic configuration of
`O^(2-)` is,
`1s^22s^22p^6`

The number of electrons in
`O^(2-)` = 10

From this we conclude that, the option 1, 2, 3 and 5 have the same number of electrons as the neutral atom of neon. While in 'Ar' there are 18 number of electrons.

Hence, the correct option is, Ar