The element whose electron configuration is shown is boron. Boron is in group 13 of the periodic table.
From the question, we are to complete the missing parts in the electron configuration of boron. The group 13 elements have outermost electron configuration of ns2 np1.
For boron;
A = 2
B= 1
Hence boron has a complete electronic configuration of 1s2 2s2 2p1.
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