How many grams of kno3 should be used to prepare 2.00 liter of a 0.50 m solution

Mr of KNO3 = 101. 

n = cv where n is moles, c is concentration (in this case 0.5 moles for every litre) and v is the volume 

your moles would be 0.5 x 2 =1 

and since n (moles) = m/mr and your mole is 1 .. your mass would be 101g

Hope I answered your question! :) 

A.