The moles can be defined as the mass of the substance with respect to molar mass. The moles of potassium nitrate is 1 mol.
<h3>How to calculate moles of a substance?</h3>
The moles of a compound can be calculated from:

The molarity can be defined as the moles of solute in a liter of solution.
The molarity can be expressed as:

The molarity of potassium nitrate solution is 2 M, and the volume is 500 mL.
The moles of potassium nitrate is given as:

The moles of potassium nitrate in 2 M, 500 mL solution are 1 mol.
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The balanced chemical formula should be Al2(SO4)3 + 6NaOH = 2Al(OH)3 + 3Na2SO4
Therefore the coefficient of Al(OH)3 is 2!
Hope that helps :)
Answer is in a photo. I can only upload it to a file hosting service. link below!
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Im sorry , Im confused reading this . maybe enter a image ?