The electron dot symbol for chlorine has the symbol Cl surrounded by 7 dots (two each on three sides and one on
the fourth side). Another element that could be represented
by an identical electron dot arrangement would have which
of the following atomic numbers?
19
а
b
10
11
C С
d
9
7
e

The correct option is 9

Explanation:

The number of dots in the electron dot symbol for chlorine = 7

The arrangement are 2 each on three of the for sides and one dot on the forth side

Therefore, given that the electronic configuration of the different orbital levels are;

1st = 1s²

2nd = 2s²2P⁶

The element that will have 7 electrons in the outermost shell similar to that of chlorine will have an electronic configuration as follows;

1s²2s²2P⁵, such that there are a total of 9 electrons (2 + 2 + 5 = 9) with 7 of the electrons in the outermost shell and 7 dots surrounding the element's symbol

However, since the for the atom to be electronically neutral, there are equal number of electrons and protons in the atom and given that the atomic number = The number of protons in the nucleus of the atom, we have that the atom having 7 dots surrounding its symbol similar to chlorine, Cl, has an atomic number of 9.

i believe you are right for all except the 3rd ( look at sqdancefan his answer is much better)