I really need help on this please, I think C or A, but I don't really know??!

What is a metal replacement reaction

Which of the following represents the ester functional group? a. -coo- b. -cho c. -cooh d. c=o

If it is an isoelectronic series select true, if not select false. o2-, s2-, se2-, te2- na+, k+, rb+, cs+ n3-, p3-, as3-, sb3- ag, cd+, sn3+, sb4+ f-, cl-, br-, i- f-, ne, na+, mg2+ s2-, s, s6+