Water cycle simply refers to the continuous movement or flow of water from the atmosphere to the earth and back to the atmosphere
<h3>What is are the stages of water cycle?</h3>
These are the basic stages through which water passes. These stages are:
-  Evaporation
 - Condensation
 - Precipitation 
 - Collection. 
 
So therefore, water cycle simply refers to the continuous movement or flow of water from the atmosphere to the earth and back to the atmosphere
Learn more about water cycle:
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49 neutrons in each nucleus.
<h3>Explanation</h3>
For each nucleus:
Mass number = Number of protons + Number of neutrons.
The atomic number of a nucleus is the same as its number of protons. The atomic number of the nucleus here is 31. There are 31 protons in each nucleus.
- Mass number = 80;
 - Number of protons = Atomic number = 31;
 - The number of neutrons is to be found.
 
Again,
Mass number = Number of protons + Number of neutrons.
80 = 31 + Number of neutrons.
Number of neutrons = 80 - 31 = 49.
 
        
             
        
        
        
<h3>1</h3>
Species shown in bold are precipitates.
- Ca(NO₃)₂ + 2 KOH → Ca(OH)₂ + 2 KNO₃
 - Ca(NO₃)₂ + Na₂C₂O₄ → CaC₂O₄ + 2 NaNO₃
 
- Cu(NO₃)₂ + 2 KI → CuI₂ + 2 KI
 - Cu(NO₃)₂ + 2 KOH → Cu(OH)₂ + 2 KNO₃
 - Cu(NO₃)₂ + Na₂C₂O₄ → CuC₂O₄ + 2 NaNO₃
 
- Ni(NO₃)₂ + 2 KOH → Ni(OH)₂ + 2 KNO₃
 - Ni(NO₃)₂ + Na₂C₂O₄ → NiC₂O₄ + 2 NaNO₃
 
- Zn(NO₃)₂ + 2 KOH → Zn(OH)₂ + 2 KNO₃
 - Zn(NO₃)₂ + Na₂C₂O₄ → ZnC₂O₄ + 2 NaNO₃
 
<h3>2</h3>
A double replacement reaction takes place only if it reduces in the concentration of ions in the solution. For example, the reaction between Ca(NO₃)₂ and KOH produces Ca(OH)₂. Ca(OH)₂ barely dissolves. The reaction has removed Ca²⁺ and OH⁻ ions from the solution. 
Some of the reactions lead to neither precipitates nor gases. They will not take place since they are not energetically favored.
<h3>3</h3>
Compare the first and last row:
Both Ca(NO₃)₂ and Zn(NO₃)₂ react with KOH. However, between the two precipitates formed, Ca(OH)₂ is more soluble than Zn(OH)₂. 
As a result, add the same amount of KOH to two Ca(NO₃)₂ and Zn(NO₃)₂ of equal concentration. The solution that end up with more precipitate shall belong to Zn(NO₃)₂.
<h3>4</h3>
Compare the second and third row:
Cu(NO₃)₂ reacts with KI, but Ni(NO₃)₂ does not. Thus, add equal amount of KI to the two unknowns. The solution that forms precipitate shall belong to Cu(NO₃)₂.