Fill in the blanks.
(i) The range of the data: 15, 4, 16, 20, 5, 6, 16, 8, 2, 1, 19, 0, is __P__.
(ii) Probability of an impossible event is __Q__.
(iii) The number of times a particular observation occurs in given data is called __R__.
(iv) In a single throw of two dice, the probability of getting a total of 11 is __S__.