Molarity = Moles of solute / Volume of solution in liter

Moles of NaCN = 50 g/49gmol?¹ = 1.0204 mol     ( Molecular weight of NaCN = 49)

Volume of solution in liters  = 500mL/1000mL

Molarity =1.0204 mol * 1000mL l^-1/500mL

               =2.0408M = 2.0408 mol L^-1=2.0408 mol dm ^–3

% w/v is the mass of the solute dissolved in 100mL of the solution

500mL solution contains 50g NaCN

Therefore, 100mL contains =100*50/500= 10g/100mL

%w/v = 10

Parts per million (ppm) = (Number of parts of the component/ Total number of parts of all component of the solution)*10⁶

=(50/500)*10⁶

NCERT chemistry class XII unit 2 has all these formulae, its easy by practice u will understand it.