The correct option is A.
The elements in the periodic table are arranged into groups and columns on the basis of their atomic number. Elements with similar number of electrons in their outermost shells fall in the same group of the periodic table. There are some properties of the elements that changes both in the periods and the groups of the periodic table and one of these is conductivity. Conductivity increases across period 3 from sodium to aluminium and then decrease to silicon. Thus, sodium is a good conductor of electricity.
