Question

All elements in the third period have :
A. Three Complete shells
B. Three complete subshells
C. Three valence electrons
D. Three electrons less than octet
Plzzz answer fast!! Plzzz!

Answer 1

B is the correct answer as third period starts from Na sodium(11)
=> 1s^2 , 2s^2 , 2p^6, 3s^1...
So it have minimum three complete subshell (1s, 2s and 2p)..

Answer 2

The principal quantum number of valance electron represents the period of the element. hence,
hence, all elements of third period represent outermost shells of elements .

we know,
according to Bohr's theory
in K - shell = 2 electrons
in L- shell= 8 electrons
in M - shell = 18 electrons.

but in third period maximum number of electrons = 18 ( Ar)
1s² => first shell
2s² , 2p^6 => 2nd shell
3s² , 3P^6, 3d^10=> 3rd shell .

we see last element ( e.g Ar) configuration = 1s², 2s²,2P^6 3s², 3p^6, 3d^0
hence, 3rd shell incomplete , hence option (A) is incorrect .

now , configuration of first element ( e.g Na) = 1s², 2s², 2p^6, 3s¹
we see three subshell ( 1s, 2s , 2p) are complete so, option (B) is correct .
option (C) is incorrect becoz period doesn't depends upon valance electrons .option (D) is also incorrect.

hence, option (B) is correct .