The reaction between copper II chloride and sodium sulfide as well as lead II nitrate and potassium sulfate both produce precipitates.
The solubility of a substance in water is in accordance with the solubility rules.  It is possible that a solid product may be formed when two aqueous solutions are mixed together. That solid product is referred to as a precipitate.
Now, we will consider each reaction individually to decode whether or not a precipitate is possible. 
- In the first reaction, we have; CuCl2(aq) + Na2S(aq) ---->CuS(s) + 2NaCl(aq). A precipitate (CuS) is formed.
- In the second reaction, Pb(NO3)2(aq) + 2KNO3(aq) ----> PbSO4(s) + KNO3(aq), a precipitate PbSO4 is formed
- In the third reaction, NH4Br(aq) + NaOH(aq) ----->NH3(g)  + NaBr(aq) + H2O(l), a precipitate is not formed here.
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The pressure in a sealed container means the volume of container is fixed
so we cannot change the volume of container hence gas
The other factors which can affect the pressure are
a) moles of gas : if we increase the moles of gas the pressure of gas will increase
b) Temperature: if we increase the pressure of gas the pressure of gas will increase due to increase in kinetic energy
So the following cannot increase pressure
a) decrease in moles of gas
b) decrease in temperature of gas
 
        
                    
             
        
        
        
Since the given formula is . According to cross method formula, magnesium has +2 charge so, is multiplied by 2.
Thus, 1 molecule of magnesium phosphate will contain 2 atoms of phosphorus.
Therefore, three molecules of magnesium phosphate contains following number of atoms.
Mg = 9
P = 6
O = 24
Hence, we can conclude that there are 6 atoms of phosphorus in three molecules of magnesium phosphate, .
        
             
        
        
        
different parts of the sum rotate at different rates