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Answer: Wheel and Axle
Both of these work together to form a simple machine. You can't have one without the other.
If you try to turn just the axle itself, then you'll find it takes a lot of work. This is because the inertia of the axle wants to keep the object at rest. Also, you won't have a lot of torque due to the small radius compared to what a doorknob can offer.
Using a doorknob is like putting a (steering) wheel on an axle. This increases the radius and therefore increases the torque. You put in less work into the system and get more out of it.
The best option is melting point
Answer: A strong acid like HCl dissociates completely in an aqueous solution.
By definition a strong acid is that that dissociates completely in aqueous solutions. That means that all the molecules of the acid will be inoized into hydronium cation (H3O+) and anion (the negative radical).
For expample, HCl is a strong acid because
HCl + H2O----> H3O(+) + Cl-
The forwar arrow indicates that all the molecules of HCl reacted with the water for form the ions.
