CBSE Class 10 Science 2019 · Paper 31/2/1 · Question 16(b)
The electrons in the atoms of four elements A, B, C and D are distributed in three shells having 1, 3, 5 and 7 electrons respectively in their outermost shells. Write the group numbers in which these elements are placed in the Modern Periodic Table. Write the electronic configuration of the atoms of B and D and the molecular formula of the compound formed when B and D combine.
Answer
The groups are 1, 13, 15 and 17; B is and D is , forming .
Group numbers: A (1 valence electron) is in group 1, B (3) in group 13, C (5) in group 15 and D (7) in group 17.
Electronic configurations: B = 2, 8, 3 and D = 2, 8, 7.
Formula: B has valency and D has valency , so the compound formed is . (A, B, C and D are sodium, aluminium, phosphorus and chlorine, so is .)
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