The correct option is C 16th group and 2nd period
Electronegativity is the tendency of an atom to gain electron(s) in order to attain noble gas configuration. Since it decreases down the group and increases across a period from left to right, fluorine has the highest electronegativity in the periodic table.
Comparing the electronegativity of oxygen and chlorine, we see that electronegativity of oxygen is higher than that of chlorine. This is because chlorine has an extra shell (energy level) and the nuclear force of attraction is low compared to that of oxygen.
Thus, element X is oxygen and has the second highest electronegativity. It belongs to the 16th group and 2nd period of the periodic table.