One mole of a substance is equal to 6.022 × 10²³ units of that substance (such as atoms, molecules, or ions). The number 6.022 × 10²³ is known as Avogadro's number or Avogadro's constant. The concept of the mole can be used to convert between mass and number of particles.
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Answer:
The solubility of MnS will decrease on addition of KOH solution.
Explanation:
As per the equation given:

On dissolution of MnS in water it gives a basic solution as it gives hydroxide ions.
Now when the we are adding aqueous KOH solution, it will dissociate as:

Thus it will further furnish more hydroxide ion,
This will increase the concentration of hydroxide ions (present of product side), the system will try to decrease its concentration by shifting towards reactant side.
Thus the solubility of MnS will decrease on addition of KOH solution.