Help I am taking a test

Iknow #2 is d. i just need to know why

14. complete and balance the equations for the single displacement reactions. a. zn + pb(no3)2 -> b. al + niso4 -> 15. complete and balance the equations for the double displacement reactions. a. agno3(aq) + nacl(aq) -> b. mg(no3)2(aq) + koh(aq) -> 16. complete and balance the equations for the combustion reactions. a. __ ch4 + o2 -> b. __ c3h6 + o2 -> c. + o2 ->

Consider the four elements above. which one of these elements will combine with oxygen in a 1: 1 ratio?