Why are sodium and chlorine placed in the same period in the modern pe

1.	Why are sodium and chlorine placed in the same period in the modern periodic table
Answer» Because they are having same no. of shell in their electronic configuration Na 2,8,1 and Cl 2,8,7 and no. of shells is equal to no. of period thus they have same period 3 because it had same no. of shells as k l m

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