Hey there! :D
To some extent, all moving parts produce friction. It can be very small or minimal, but all parts produce some form of friction.
This is true.
I hope this helps!
~kaikers
4. A
because PbCl2 is an ionic compound and it's solid, so it's a substance.
It cannot be mixture, because it's a pure molecule.
5. D
despite that both substances are gases, colorless they are different molecules, so they should have different either chemical and physical properties
6. C
this substance made from W atoms and others are made from molecules
Balanced equation: 2Fe + 3H2O → Fe2O3 +3H2
Convert g to mols:
285/55.845 = 5.1034 mols
Mole ratio of Iron and Iron (III) Oxide: 2:1
5.1034/2 = 2.5517 mols
The number of grams : 17.082 g
<h3>Further explanation</h3>
Molarity shows the number of moles of solute in every 1 liter of solute or mmol in each ml of solution

Where
M = Molarity
n = Number of moles of solute
V = Volume of solution
453.9 mL of 0.237 M calcium acetate

MW Ca(C₂H₃OO)₂ : 158,17 g/mol

Answer:
The answer is C. An electrochemical cell.
Explanation:
The aluminum ion react with the sulfide to form aluminum sulfide.