Question: what are group 2 cations?
Answer: Group II (Cu2+, Bi3+, Cd2+, Hg2+, As3+, Sb3+, Sn4+) cations produce very insoluble sulfides (Ksp values less than 10-30) so they can be precipitated by low amounts of sulfide ion; this can be achieved by adding an acidic solution of H2S.