Question

If true press 1, if false press 0. 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 in the outermost shell respectively. They belong to the third period in the modern periodic table.

If true enter 1, if false enter 0

Answer 1

Since the last electron enters in the third orbital, these elements can be placed in the third period in the modern periodic table.
The element A is sodium. Its electronic configuration is $1s^{2}2s^{2}2p^{6}3s^1$. The element D is chlorine. Its electronic configuration is $1s^{2}2s^{2}2p^{6}3s^{2}3p^5$. The compound formed by the combination of elements A and D is sodium chloride. Its chemical formula is $NaCl$.