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.

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

Firstly, the water in the dams hold gravitational potential energy as they are above ground level. the gravitational potential energy is then transferred to kinetic energy as it falls, spinning the turbinethe turbine then spins the generator, which is a large magnet surrounded by metal coils. by doing this, the generator generates electricity. in this action, the energy transfer taken place is kinetic to electric energy