25)  C

Let us first find the maximum number of points 1 can score in a single round. To get the maximum score, all three darts need to land on 6.
Max score possible = 18
We know minimum score can be 0 but the question asks for scores other than 0.
Next minimum score has to be 2. It cannot be 1 because if two darts land outside, the score becomes 0.
Our range of scores = 2 to 18
To easily solve this question, we need to find the scores that we cannot score.

Remember: If a dart lands outside all of the circles, the player’s score for the turn SO FAR is halved.
So let us say the order of dart thrown was: 4, miss, 6. The total score would be 8.
After the dart lands on 4, total score so far = 4
After the dart misses, total score so far = 4/2 = 2
After the dart lands on 6, total score = 2+6 = 8

Scoring 2 = 2, 2, miss
Scoring 3 = 2, miss, 2
Scoring 4 = 4, 4, miss
Scoring 5 = 2, miss, 4
Scoring 6 = 6, 6, miss
Scoring 7 = 2, miss, 6
Scoring 8 = 4, miss, 6
Scoring 9 = 6, miss, 6
Scoring 10 = 4, 4, 2
Scoring 11 = Not possible
Scoring 12 = 4, 4, 4
Scoring 13 = Not possible
Scoring 14 = 6, 4, 4
Scoring 15 = Not possible
Scoring 16 = 6, 4, 6
Scoring 17 = Not possible
Scoring 18 = 6, 6, 6

No. of scores possible = 13