Question

Element P Q R S
Mass NO. 12 20 23 35
No. of neutron 6 10 12 18
a) write electronic configuration and atomic number
b) which of these is chemically inert

please explain how to solve

Answer 1

(a)

Atomic Number (Number of protons) :

P = 6 (12-6)

Q = 10 (20-10)

R = 11(23-12)

S = 17(35-18)

Electronic Configuration :

P = 2,4

Q = 2,8

R = 2,8,1

S = 2,8,7

(b) Note from above part that the compound Q has a configuration of 2,8 which has all shells filled and thus the compound Q is inert.

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Answer 2

Answer:

We know that:

Number of neutrons in an atom = Mass number - Atomic number

=> Atomic number = Mass number - Number of Neutrons in the atom

Now, let the elements:

With number of neutrons = 6 be A [Mass = 12]

With number of neutrons = 10 be B [Mass = 20]

With number of neutrons = 12 be C [Mass = 23]

With number of neutrons = 18 be D [Mass = 35]

Atomic number of A

Atomic number = Mass number - no. of neutrons

Z = 12 - 6

Z(A) = 6

Electronic configuration:

2,4

------

Atomic number of B

Z = 20 - 10

Z(B) = 10

Electronic configuration:

2,8

-----

Atomic number of C

Z = 23 - 12

Z(C) = 11

Electronic configuration:

2,8,1

-----

Atomic number of D

Z = 35 - 18

Z(D) = 17

Electronic configuration:

2,8,7

______

A chemically inert gas is the one which has complete number of electrons in each shell. In all the elements given, Element B is an inert gas.

Element B has:

Mass = 20

Number of neutrons = 10

__________

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