Four elements A, B, C and D have atomic numbers 12, 13, 14 and 15 respectively. Answer the following questions giving reasons:

(i) What is the number of valence electrons and valency of D?

(ii) Which of them will have largest atomic radii?

(iii) Which of these elements will form the most basic oxide?



  A B C D
Atomic Number 12 13 14 15
Electronic Configuration 2,8,2 2,8,3 2,8,4 2,8,5



Number of valence electrons in D = 5

Valency of D = 8 - 5 = 3



Because all of them have the same number of shells, A, B, C and D all belong to the same period

As we move from left to right across a period, atomic radii decreases.

A is the leftmost element, followed by B, followed by C and D is the rightmost element. 

Therefore, A will have the largest atomic size.


Since A has the largest atomic size, it will donate electrons most easily and therefore has the most metallic character . So it forms the most basic oxide.

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CA Maninder Singh is a Chartered Accountant for the past 14 years and a teacher from the past 18 years. He teaches Science, Economics, Accounting and English at Teachoo