Question

which of the two will be chemically more reactive, element X with atomic number 17 or element Y with atomic number 16?

Answer 1

Electronic configuration of y = 2, 8, 6 ⇒ belongs to 6A group
Electronic configuration of x = 2, 8, 7 ⇒ belongs to 7A group

Both the them have three shells. Therefore both of the elements belong to same period.

Across a period from left to right, chemical reactivity decreases upto 4A group and then increases.
This means the order of chemical reactivity across a period is
1A > 2A > 3A > 4A < 5A < 6A < 7A 

since, element with atomic number 17 belongs to 7A group it is is chemically more reactive than 6A group i.e element with atomic number 16.

Finally, x is more reactive than y.

Answer 2

Hi.

Here is your answer---------

Electronic configuration of X {17} = 2,8,7 
Periods = 3
Group = 7 A

Electronic configuration of Y {16} = 2,8,6
Periods = 3
Group = 6 A

Both of them have three shells, thus both belongs to the third periods . As we move from left to right Across the periods, the chemical reactivity decreases from Group 1 A to Group 4 A and then increases.

We also know, Group 6 A lie before the Group 7 A, Hence Group 6 A has a less reactivity than group 7 A. Since, the elements X is present in Group 7 A, it has more reactivity than elements Y.

For easy understanding, u can also prefer that......

From these two electronic configuration, we can observe that elements X has more reactivity than Y, since the charge of X  is 1- { one negative}, so it can easily gain electrons as compared to Elements Y. Charge of Y is 2- {two negative}, so it is less reactive than Y because it cannot easily gain electrons.

Hope it helps.

Have a nice day.