First, we must know what happens in the precipitation reaction. This type of reaction is a double replacement reactions. It is consists of two reactant compounds which interchange cations and anions to form two products. One of the products is an insoluble solid called a precipitate. For the precipitation of CaCO₃, there are two consecutive reactions involved:
1. Slaking of quicklime, CaO
    CaO + H₂O ⇒ Ca(OH)₂
2. Precipitation
    Ca(OH)₂ + CO₂ ⇒ CaCO₃ + H₂O
The ions that make up the H₂O molecule are H⁺ and OH⁻. According to solubility rules, the cation (positively charged ion) is likely to be attracted to an anion (negatively charged ion). Together, they form an ionic bond. This type of bond is when there is a complete transfer of electrons between the two. The Ca²⁺ cation lacks 2 electrons, while the anion OH⁻ has an excess 1 electron. In order to be stable, 1 Ca²⁺ ion and 2 OH⁻ ions must combine. 
Therefore, the answer is OH⁻ ion.
        
                    
             
        
        
        
To determine the pressure in units of kPa, we need to use a conversion factor to convert the units from mmHg to kPa. A conversion factor is a value that would relate two different units and is multiplied or divide to the original measurement depending on what is units is asked. From literature, 1 atm is equal to 760 mmHg and it is also equal to 101.325 kPa. We use these factors to convert the given value. We do as follows:
2150 mmHg ( 1 atm / 760 mmHg ) ( 101.325 kPa / 1 atm ) = 286.643 kPa
Therefore, the closest value from the choices is the second one which has the value of 287, this would be answer.
        
             
        
        
        
This is a physical phase change it is still water it just separated and became less and less.it stays water though
        
             
        
        
        
The answer would be decomposers
        
             
        
        
        
Compounds
Explanation:
Compounds are substances that can be broken down by chemical means. They are categorized as pure substances due to their definite composition. 
- Compounds are substances composed of two or more kinds of atoms or elements joined together in a definite grouping. 
- Properties of compounds differs from those of the constituent atoms. 
- Compounds are broken down by chemical means because they are products of chemical changes. 
- Several kinds of compounds exists through combinations of atoms. 
- Compounds have definite compositions 
Learn more: 
Compounds and bonds brainly.com/question/11064344
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