Question

Match the atomic numbers 4, 14, 8, 15 and 19 with each of the following:

1. A solid non-metal of valency 3.
2. A gas of valency 2.
3. A metal of valency 1.
4. A non-metal of valency 4. 

Answer 1

Name with valency	Atomic Number
1. A solid non-metal of valency 3	15
2. A gas of valency 2	8
3. A metal of valency 1	19
4. A non-metal of valency 4	14

Explanation: 

1. As atomic number 15 has an electronic configuration [2, 8, 5], it is a non-metal having 5 electrons in the valence shell and needs three electrons to complete its octet so it has a valency of 3.

2. As atomic number is 8, so it has the electronic configuration of [2, 6] and it needs 2 electrons to complete its octet hence, it is a gas of valency 2.

3. As atomic number 19 has an electronic configuration [2, 8, 8, 1], so it is a metal having 1 electron in the valence shell and donates its one electron to complete its octet so it has a valency 1.

4. As atomic number 14 has electronic configuration [2, 8, 4], so it is a non-metal having 4 electrons in the valence shell and needs four electrons to complete its octet so it has a valency 4.