Answer:
The electric force is conservative.
Since
ΔK = −ΔU,
Kf − Ki =Ui −Uf.
We have,
Kf = 0
Ui = 0.
Thus Ki =Uf.
<u>so ,at 10 fm Uf = (2×10)−12 J.</u>
<u>Solution</u> : Emperical Formula = 
Emperical Formula - A formula that gives the simplest whole number ratio of atom in a compound.
In the question percentages are given then assume that the total mass is 100grams so that the mass of each element is equal to the percentage given.
Given : 80.0g Carbon
20.0g Hydrogen
First convert the given masses into moles.


Value of each mole divided by the smallest number of moles and then round off.
Moles ratio of the element are


This is the mole ratio of the elements and is repersented by the subscript in the emperical formula.
Emperical Formula = 
Water is H2O but I'm not sure about solids.
Answer:
Mass of Fe produced = 4.468 g
Explanation:
Given data:
Mass of Fe produced = ?
Mass of Fe₂O₃ react = 6.50 g
Solution:
Chemical equation:
2Fe₂O₃ → 4Fe + 3O₂
Number of moles of Fe₂O₃ ;
Number of moles = mass/molar mass
Number of moles = 6.50 g/159.69 g/mol
Number of moles = 0.04 mol
Now we will compare the moles of iron and ironoxide.
Fe₂O₃ : Fe
2 : 4
0.04 : 4/2×0.04 = 0.08 mol
Mass of iron produced:
Mass = number of moles × molar mass
Mass = 0.08 mol × 55.85 g/mol
Mass = 4.468 g
yes
include sodium and potassium, dissolve instantly and dramatically in plain water — no stronger acid is needed. The metals react violently with water, releasing and igniting hydrogen gas and causing an explosion.