Identify the correct order of chemical reactivity from  the following elements?

Li<Na<K<Rb<Cs --- ionization enthalpy decreases reactivity of metals increases

I<Br<Cl<F ----electro-gain enthalpies and electro negativities increases reactivity of non metals increases

Between oxygen and chlorine, chlorine is more powerful oxidizing agent than oxygen because of much higher negative electron gain enthalpy than chlorine