Question

Suppose you have a solution that might contain any or all of the following cations: Ni2+, Ag+, Sr2+, and Mn2+. Addition of HCl solution causes a precipitate to form. After filtering off the precipitate, H2SO4 solution is added to the resultant solution and another precipitate forms. This is filtered off, and a solution of NaOH is added to the resulting solution. No precipitate is observed.

Answer 1

Ni2+, Ag+, Sr2+, and Mn2+, & with the Addition of HCl --> AgCl ppts 


Ni2+, Sr2+, and Mn2+, & with the Addition of H2SO4 --> SrSO4 ppts 


Ni2+, and Mn2+, & with the Addition of NaOH --> both Mn(OH)2 & Ni(OH)2 would have ppt'd 
but since no ppt,... 
there was no Ni+2 or Mn+2 

your answers are 
Ag+ & Sr+2 were present 
& 
Ni+2 & Mn+2 were not present