Answer : The correct option is, (D) They have the same number of electrons in their outermost shells.
Explanation :
Periods : A row in the periodic table is known as periods.
The common features about the elements of a period are :
Each periods has elements with the same number of electron shells or energy levels or shell.
They transition from metal to noble gas that means they move from metal to non-metal and then non-metal to noble gas.
Groups : A column in the periodic table is known as groups.
The common features about the atoms of elements in a same group are :
Each groups has elements with the same number of valance electrons or have same of electrons in their outermost shells.
The elements in the same group have similar chemical properties.
The elements in the same group have similar physical properties.
Hence, the correct option is, (D) They have the same number of electrons in their outermost shells.
