Q10 of 59 Page 1

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'.

Given: mass of number of X = 35


No. of neutrons = 18


Atomic number of element X = Mass number – no. of neutrons present


Atomic no. = 35 -18 = 17


The electronic configuration of X will be 2, 8, 7


X will belong to group no. 10 + 7= 17th


X will belong to period 3rd as it has three shells.


Since it requires one more electron to get stable gas electron configuration, so the valency is 1.


'X'


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