Explanation:
The given elements Na, Al, P and Cl are all elements of period 3.
Atomic number of sodium is 11 with electronic distribution 2, 8, 1.
Atomic number of aluminium is 13 with electronic distribution 2, 8, 3.
Atomic number of phosphorous is 15 with electronic distribution 2, 8, 5.
Atomic number of chlorine is 17 with electronic distribution 2, 8, 7.
An element that has the tendency to readily attract an electron towards itself is known as an electronegative element.
So, out of the given elements chlorine is the most electronegative. Hence, an electron will be most strongly attracted to chlorine.