Question

14. The elements A, B, C and D have atomic numbers 4, 11, 12 and 19 respectively.

Which pair of element belongs to the same period?​

Answer 1

Answer:

Elements B and C belongs to the same period.

Explanation:

Given that A, B, C and D have atomic numbers 4, 11, 12 and 19 respectively.

Elements are placed in the same period when they have same number of atomic shells.

So, let's find out the electronic configuration of each element to find out the number of shells.

✿ For Element A:

• Atomic number = 4
• Electronic configuration = 2, 2

So, there are only 2 shells for Element A

✿ For Element B:

• Atomic number = 11
• Electronic configuration = 2, 8, 1

So, there are 3 shells for Element B.

✿ For Element C:

• Atomic number = 12
• Electronic configuration = 2, 8, 2

So, there are 3 shells for Element C.

✿ For element D:

• Atomic number = 19
• Electronic configuration = 2, 8, 8, 1

So, there are 4 shells for Element D.

The elements which have the same number of atomic shells are placed in same period.

So, B and C are placed in same period.

Answer 2

Element with atomic no. 11(Na) and 12(Mg) belong to same period.

Element with atomic no. 4(Be) and 12(Mg) belong to same group.