Question

Match the atomic number 2,4,8,15 and 19 with each of the following
(i) A solid non-metal belonging to the third period.
(ii) A metal of valency 1.
(iii) A gaseous element with valency 2.
(iv) An element belonging to group 2.
(v) A rare gas.

Column 1	Column 2
A solid non-metal belonging to the third period.	2
A metal of valency 1 .	4
A gaseous element with valency 2 .	8
An element belonging to group 2 .	15
A rare gas.	19

Answer 1

Part 1: Non-metal belonging to period 3:-

1. The element with atomic number 15 is Phosphorous.
2. Its electronic configuration is $2,8,5$
3. Hence it belongs to period 3.

Part 2: Metal with valency 1:-

1. The element with atomic number 19 is Potassium.
2. Its electronic configuration is $2,8,8,1$
3. Since it has only 1 electron in its outermost shell, therefore its valency is 1.

Part 3: A gaseous element with valency 2:-

1. The element with atomic number 8 is Oxygen.
2. Its electronic configuration is $2,6$
3. Since it has 6 electrons in its valence shell, therefore its valency is 2.
4. Oxygen is gaseous in nature.

Part 4: An element belonging to group 2:-

1. The element with atomic number 4 is Beryllium.
2. Its electronic configuration is $2,2$
3. Since it has 2 electrons in its valence shell, therefore it belongs to group 2.

Part 5: A rare gas:-

1. The element with atomic number 2 is Helium.
2. Its electronic configuration is $2$
3. It is a noble gas and is non-reactive.
4. It is very rare in nature and naturally occurs in gaseous state.

Hence,

Column I	Column II
(i) A solid non-metal belonging to the third period.	15
(ii) A metal of valency 1 .	19
(iii) A gaseous element with valency 2 .	8
(iv) An element belonging to group 2 .	4
(v) A rare gas.	2