The electro negativity of selanium is greater than oxygen..why..??.but the electronegativity of bromine is less than flourine..why..??
This is not correct. Electronegativities for Oxygen and Selenium by Pauling scale are of 3.44 and 2.55, respectively. As Oxygen is located in the top of group, it has smaller radius and strong ability to attract electrons. Therefore, Selenium with larger radius has lower electronegativity than Oxygen. The same tendency is found for F, Cl, Br, which reveal electronegativities of 3.98, 3.16 and 2.96, respectively.