Which pair of elements would most likely bond to form a covalently bonded compound?

Compounds a and b react to form compounds c and d according to the equation: aa + bb → cc + dd. under which conditions will the rate law be given by the equation: rate = k[a]a[b]b? a. the reaction takes place in one step. b. the reaction is endothermic. c. the reaction is exothermic. d. the reaction involves more than one step.