Given:

V = ? ,  C = 0.100M, m = 5g 

Molar mass, M of NaNO\(_3\) = 23 + 14 + (16 X 3) = 85 g/mol

Number of moles, n = \(\frac{mass}{Molar Mass}\)

  = \(\frac{5}{85}\)

 n = 0.0588 mole

Recall that  n = \(\frac{CV}{1000}\) 

 n = CV (looking through the options, no need including the 1000 since the answer was left in Litres)

  V = \(\frac{n}{C}\)

  V =  \(\frac{0.0588}{0.100}\)

  V =  0.588 Litres