The type of reaction that occurred in the test tube is ACID BASE REACTION.
Acid base reaction is a type of chemical reaction in which an acid and a base react together to form salt and water molecules. It is also known as neutralization reaction. For the question given above, the applicable chemical reaction is as follows:
HF + NaOH = NaF + H2O
From this chemical reaction, it can be seen that, hydrogen fluoride, which is a weak acid react with sodium hydroxide which is a strong base to produce sodium fluoride, which is a salt and a molecule of water.
We can use the law of conservation of energy to solve the problem.
The total mechanical energy of the system at any moment of the motion is:

where U is the potential energy and K the kinetic energy.
At the beginning of the motion, the ball starts from the ground so its altitude is h=0 and therefore its potential energy U is zero. So, the mechanical energy is just kinetic energy:

When the ball reaches the maximum altitude of its flight, it starts to go down again, so its speed at that moment is zero: v=0. So, its kinetic energy at the top is zero. So the total mechanical energy is just potential energy:

But the mechanical energy must be conserved, Ef=Ei, so we have

and so, the potential energy at the top of the flight is
Answer:
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Explanation:
4 degrees C turns out to be the temperature at which liquid water has the highest density. If you heat it or cool it, it will expand. ... Ice floats on top of lakes, preventing evaporation (and convection in the frozen layer), and lakes stay liquid underneath, allowing fish and other life to survive.