Solution:
For each event to be a valid assignment of probability,
Each event in sample space should have a probability of less than 1, and the total probability of all occurrences should be exactly equal to 1.
(i) Valid.
As each $P (w_i)$ (for i=1 to 7) lies between 0 to 1 and sum of $P (w_1) =1$
(ii) Valid.
As each $P (w_i)$ (for i=1 to 7) lies between 0 to 1 and sum of $P (w_1) =1$
(iii) Not valid.
As sum of $P (w_i) = 2.8$ which is greater than 1
(iv) Not valid.
As $P (w_7) = 15/14$ which is greater than 1