1. NiCl₂ + 2NaOH = Ni(OH)₂↓ + 2NaCl
Ni²⁺ + 2Cl⁻ + 2Na⁺ + 2OH⁻ = Ni(OH)₂↓ + 2Na⁺ + 2Cl⁻
Ni²⁺ + 2OH⁻ = Ni(OH)₂
2. MgCO₃ + 2HNO₃ = Mg(NO₃)₂ + CO₂↑ + H₂O
MgCO₃ + 2H⁺+ 2NO₃⁻ = Mg²⁺ + 2NO₃⁻ + CO₂↑ + H₂O
MgCO₃ + 2H⁺ = Mg²⁺ + CO₂ + H₂O
3. Zn(NO₃)₂ + H₂S = ZnS↓ + 2HNO₃
4. ZnCl₂ + H₂S = ZnS↓ + 2HCl