No. of mol of NaOH used = 8/40 = 0.2 mol
100 cm³ = 0.1 dm³
Concentration of solution in mol/dm³ = 0.2/0.1 = 2 mol/dm³
regarding ur working, 8/40X(24)
u can only multiply by 24 dm³ when it is a GAS
the 40 (Mr of NaOH) is NOT the NUMBER OF MOLES, it is the molecular
mass of 1 mole of NaOH, therefore even if it is a gas, u are
wrong
the 8g is only the amt of NaOH used, not the number of moles of
NaOH used, so u need to divide 8g by the Mr of NaOH
hope this helps 
