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 Modem 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.

A – 1st group.
B – 13th group.
C – 15th group.
D – 17th group.
Electronic configuration of B (Atomic number = 13) is (2 8 3).
D (Atomic number = 17) is 2 8 7.
Hence, the molecular formula of the compound when B and D combine is BD3.

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