Explanation:
25g in NaCl dissolved in 500 ml of water
M(NaCl) = 58,44 g/mol
n1(NaCl) = m(NaCl) / M(NaCl)
n1(NaCl) = 25 / 58,44
n1(NaCl) = 0,428 mol
C1 = n1(NaCl) / V
C1 = 0,428 / 0,500
C1 = 0.856 mol/L
10% solution of NaCl
10% solution of NaCl means 10 g of NaCl for 100g of water
therefore : 50 g of NaCl for 500 g of water (1,00L)