An aqueous solution contains 0.28 M nitrous acid . One Liter of this solution could be converted into a buffer by the addition of: (Assume that the volume remains constant as each substance is added.) 0.28 mol NaI 0.29 mol NaNO 2 0.14 mol HI 0.29 mol HI 0.070 mol Ca(OH) 2 Solution A buffer solution is mixer of weak acid and it\'s salt with strong base or vice-versa. In the given statement HNO2 is weak acid so inorder to make a buffer we must add a salt with strong acid here it is NaNO2. So 0.29 mol NaNO2 was added to 0.28 M HNO2 .