The answer is the 3rd one
Answer:
Eutrophication is the enrichment of a body of water with excessive nutrients (nitrogen and phosphorus), which causes algal growth and subsequent decline of dissolved oxygen after decomposition.
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(NH4)2CO3(aq)+ZnCl2 (aq)-----> ZnCO3(s)+2NH4Cl(aq)
Zn²⁺ +CO3²⁻-----> ZnCO3