The two are potassium and rubidium. Why? Na is an alkali metal. As you go down the metals become more reactive. 
Calcium has 20 protons. Why? The atomic # is 20 (the one at the top). 
It has 20 neutrons. Why? The atomic mass (the number on the bottom) is ~40, ignoring electron mass. 40- 20 protons = 20 neutrons. 
It has 20 electrons. 
Why? The # of protons and electrons is the same. Ions aren't on the periodic table.
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<em>The Jan. 21</em> total lunar eclipse will be the last one until May 2021, and the last one visible from the United States until 2022; the most recent total lunar eclipse previous to this one appeared in July 2018.
 
        
                    
             
        
        
        
Answer:
xylem cell and phloem cell 
 
        
             
        
        
        
Answer:
Water can carry many different kinds of bacteria and possible diseases. It is important to treat the water correctly so these are not consumed. Having good water quality means having safe water to drink for all.
Explanation:
 
        
             
        
        
        
Hello,
Here is your answer:
The proper answer to this question is "vacuoles are used to clean the cell for example a child cleaning his or her room they would put his or her toys into a closest and that was a vacuole does it cleans up things in a cell and keeps them stored into there like a closest".
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