Like Surds: Like surds are those surds which has same radicand.
Unlike surds: Unlike surds are those surds which has different radicand.
a){√8,√12,√20,√54} can be written as {2√2,2√3,2√5,3√6}-- since radicands are different so it is a set of unlike surds.
b){√50,3√54,4√32,} can be written as {5√2,3√2,2√2} --since radicands are same so it is a set of like surds.
c){√8,√18,√32,√50} can be written as {2√2,3√2,4√2,5√2}--since radicands are same so it is a set of like surds.