Question

1. choose the best answer.

which type of reaction is this?
cdso₄(aq) + k₂s(aq) → k₂so₄(aq) + cds(s)
options: acid - base, redox, precipitation

Explanation:

Step1: Analyze Reaction Type

First, recall reaction types: acid - base (involves H⁺/OH⁻ or proton transfer), redox (change in oxidation states), precipitation (formation of insoluble solid from aqueous solutions). The reaction is \( \ce{CdSO_4(aq) + K_2S(aq) -> K_2SO_4(aq) + CdS(s)} \). Here, \( \ce{CdS} \) is a solid (precipitate) formed from two aqueous solutions. Oxidation states: Cd in \( \ce{CdSO_4} \) is +2, in \( \ce{CdS} \) is +2; S in \( \ce{K_2S} \) is -2, in \( \ce{CdS} \) is -2; K is +1, S in \( \ce{SO_4^{2 - }} \) is +6. No redox change. Not acid - base (no H⁺/OH⁻ transfer). So it's a precipitation reaction (double - displacement with precipitate formation).

Step2: Eliminate Other Options

• Acid - base: No H⁺ or OH⁻ involved, so not acid - base.
• Redox: Oxidation states of all elements remain same, so not redox.
• Precipitation: Forms insoluble \( \ce{CdS(s)} \) from aqueous reactants, so this is correct.

Answer:

precipitation (the option corresponding to "precipitation" in the multiple - choice, e.g., if the third option is "precipitation", then the answer is the third option with label, e.g., C. precipitation (assuming the options are labeled A: acid - base, B: redox, C: precipitation))