An element X has mass number 35 and number of neutrons 18. Write atomic number and electronic configuration of `X´. Also write group number, period number and valency of `X´.

argon

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how can element b argon is it chlorine

it belongs to group 17.period 3.
Chlorine atomic no 17 
Electronic configuration=2,8,7

Mass number =35 Number of neutrons=18 Mass Number - No. of Neutrons = No of Protons No. Of Protons = 35 -18 No. Of Protons = 17 No. Of Electrons = No. Of Protons No. Of Electrons = 17 Atomic No. = 17 (2,8,7) Group No. = 17 Period Number = 3rd Valency = 1

Atomic no.of x=mass no of x- no. Of neutrons
=35 - 18=17
So,atomic number of x is 17.
Therefore,electric confihuration of x is 2,8,7

Group -17
Period- 3 .

atomic nos :- 17
elc cngf :- 2,8,7
grp nos :- 17
perriod nos :-3

find the number of neutrons in the nucleus

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so pls study

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Atomic number of X=mass no of X — no of neutrons = 35–18 =17 Atomic number of X is 17 Electronic configuration is 2,8,7 Group no is 7 or 17 Period no is 3 because there are 3 periods Valency is 1 ( because 7 electrons are in outer most shell only one electron is needed to be stable so the valency is 1

The mass number is the number of protons + the number of neutrons.
The mass number of element X is said to be 35 and the number of neutrons is given to be 18.
Hence, 35 = no. of protons + 18
            35 - 18 = no. of protons
            17 = no. of protons
We can conclude that, the element has an atomic number of 17 as the number of electrons is equal to the protons and the number of electrons gives the atomic number.
The electronic configuration is:- 2 , 8 , 7. It has a valency 1 and can gain one more electron to attain stability.
The element having atomic number 17 is chlorine.
The number of shells gives the period number,  element X having 3 shells lies in the third period.
It lies in the 17th group