In the given reaction potassium metal is placed in water and when a reactive metal is placed in water, it reacts with water to form metal hydroxide and hydrogen gas, as a result, potassium hydroxide and hydrogen gas are produced in the reaction. A redox reaction is a reaction in which a substance is oxidized during the reaction whereas some other substance is reduced during the reaction, simultaneously.
The given chemical reaction is:
2K(s) + 2H20(l) arrow 2KOH(aq) + H2(g)
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They vibrate back and forth
First we must write a balanced chemical equation for this reaction

The mole ratio for the reaction between
and
is 1:2. This means 1 moles of
will neutralize 2 moles
. Now we find the moles of each reactant based on the mass and molar mass.



The
was enough to neutralize the acid because 18.87:39.67 is the same as 1:2 mol ratio.
The given compound is 
Each formula unit of
has 2 mol Potassium (K) atoms, 2 mol Chromium (Cr) atoms and 7 mol Oxygen (O) atoms.
Atomic weight of potassium is 39.0983 amu
Atomic weight of Chromium is 51.9961 amu
Atomic weight of Oxygen is 15.9994 amu.
Therefore the formula weight of 

= 294.1846 amu
Velocity = change in displacement/ change over time
V = 27/ 2 = 13.5m/s