<span>Hydroelectric energy uses the movement of water to spin a turbine and produce electricity. Coal is a fossil fuel that is burned as an energy source, which results in emissions such as carbon dioxide, nitrogen, and sulfur. Coal use is associated with waste products both from the mining process to acquire the coal and also from the actual use of coal itself. Hydroelectric energy does not involve waste, but does pose potential problems to waterways. Coal use is more common than the use of hydroelectric energy.</span>
Answer: 
Explanation: A double displacement reaction is one in which exchange of ions take place.
The compounds which are soluble in water are designated by symbol (aq) and those which are insoluble in water and remain in solid form are represented by (s) after their chemical formulas.
Thus the exchange of ions take place and all the compounds are soluble so the chemical formulas are followed by the symbol (aq).
Hey there!
C₅H₅ + Fe → Fe(C₅H₅)₂
Put a coefficient of 2 in front of C₅H₅ on the left side because there is a subscript of 2 after C₅H₅ in parenthesis on the right.
2C₅H₅ + Fe → Fe(C₅H₅)₂
Fe (iron) is already balanced since there is one on each side, so we don't need to change anything for that.
This is a synthesis reaction because two reactants, C₅H₅ and Fe, are yielding a single product, Fe(C₅H₅)₂.
Hope this helps!
Mass number = protons + neutrons
mass number = 5 + 7
mass number = 12
