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! :)
