Question

An element 'X' has mass number 35 and the number of neutron is 18. Indentify the group number and period of 'X' ?

Answer 1

Hello!

Here is your answer!
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Given :

Mass number of element is 35
Number of neutrons= 18

Formula to find number of protons: 
Mass number = number of protons + number of neutrons.
35=× +18
×=35 - 18
X=17.
Number of protons =17 and number of electrons also will be 17 as atom is electrically neutral.

Hence Element is chlorine

Electronic configuraton:
1s2 2s2 2p6 3s2 3p5

Group number= 17
Period number =3
Valency =1
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Hope it helps!

Answer 2

Answer:

We know :

Atomic number = Mass number - No. of neutrons.

Atomic number = 35 - 18

= > 17

Electronic configuration :

2 , 8 , 7

Group no. = 17

Period no. = 3

Name of element is Chlorine (  Cl ) .