Separate soul.ions of sodium salts NaW, NaX, NaY and NaZ have pH 7.0, 9.0, 10.0 and 11.0 respectively, when each solution was 0.1 M. The strongest acid is :

pH of NaW⇒7
pH of NaX⇒9 (X is a weak acid, i.e. pH of NaX is basic)
pH of NaY⇒10
pH of NaZ⇒11
Thus,

W = stronger acid because pH is near to neutral.
So, HW will be the strongest acid