Question

Rohit categorized the elements P, Ar, B and Al into categories:
Category I: Elements with same valency
Category II: Elements with same number of shells
Select the option with correct categorisation of the given elements?
${\text{A}}{\text{. I}} \to P,B,Al{\text{; II}} \to P,Ar,Al$
${\text{B}}{\text{. I}} \to Al,B{\text{; II}} \to P,Ar,Al$
${\text{C}}{\text{. I}} \to Ar,B{\text{; II}} \to P,Al$
${\text{D}}{\text{. I}} \to P,Al{\text{; II}} \to B,Ar$

Answer 1

Hint – First write the electrons per shell and then observe the valency of each of the elements given, i.e., P, Ar, B and Al.

Complete answer:
We have been given four elements P, Ar, B and Al.
Now, the first category is of elements with the same valency and the second category is of elements with the same number of shells.
Now, Electrons per shell of the following elements-

• 1. Phosphorus (P) –

K	L	M
2	8	5

2. Aluminium (Al) –

K	L	M
2	8	3

3. Boron (B) –

K	L
2	3

4. Argon (Ar) –

K	L	M
2	8	8

Now, as we can see that the valency of P, Al, B is the same, as P gains 3 electrons to complete its octet and Al loses 3 electrons and B shares its 3 electrons to complete its octet.
So, P, Al, B belongs to category I.
Now, phosphorus, argon and aluminium belong to the third period and have three shells i.e., K, L and M.
Therefore, P, Ar and Al belong to category II.

Hence, the correct option is A.

Note – Whenever such types of questions appear then always first write the electronic configuration as mentioned in the solution, and then as we can see the valency of P, Al and B is same, so they belong to the third category and the elements P, Ar and Al belongs to category II as they have same number of shells.