Respuesta :

 as, molarity = number of moles of solute / volume of solution(in liter) 
here, volume is 500ml or 0.5 l 
molarity is 0.04M 
no. of moles of solute = mass of NaOH required (x) / gram atomic mass of NaOH(=40) 

therefore, 0.04 = x / (40 x 0.5) 
x = 0.8gram