Question

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 and valency of X.

Answer 1

we know that -
number of neutrons = atomic mass + number of protons
so,
number of proton = atomic mass - number of neutron
then,
number of proton = 35 - 18 = 17
now,
we know that -
number of proton = number of electrons
so,
number of electron = 17
And number of electrons = Atomic number .

The electronic configuration of this element is -
1s^2 2s^2 2p^6 3s^2 3p^6 .

Now, we can identify the element it is CHLORINE and it comes in Group III and period III .

Its valency is (- 1 ) because it has 7 electrons in its outermost shell so it will accept one electron from any element and get stabilize.

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