2, 3.1, 5.3, 8.6, 13, 18, 25.1

Options

A. 3.1
B. 2
C. 5.3
D. 18

Explanation

To find the odd one out in the series: 2, 3.1, 5.3, 8.6, 13, 18, 25.1, we will analyze the pattern in the differences between consecutive terms.

### Step-by-Step Solution:

1. **Identify the Series:**
The series given is:
\[ 2, 3.1, 5.3, 8.6, 13, 18, 25.1 \]

2. **Calculate the Differences:**
We will calculate the differences between consecutive terms:
- Difference between 3.1 and 2:
\[ 3.1 - 2 = 1.1 \]
- Difference between 5.3 and 3.1:
\[ 5.3 - 3.1 = 2.2 \]
- Difference between 8.6 and 5.3:
\[ 8.6 - 5.3 = 3.3 \]
- Difference between 13 and 8.6:
\[ 13 - 8.6 = 4.4 \]
- Difference between 18 and 13:
\[ 18 - 13 = 5 \]
- Difference between 25.1 and 18:
\[ 25.1 - 18 = 7.1 \]

3. **List the Differences:**
The differences we calculated are:
\[ 1.1, 2.2, 3.3, 4.4, 5, 7.1 \]

4. **Identify the Pattern:**
The pattern in the differences appears to be:
- The first difference is \(1.1\) (which is \(1.1\)),
- The second difference is \(2.2\) (which is \(1.1 + 1.1\)),
- The third difference is \(3.3\) (which is \(2.2 + 1.1\)),
- The fourth difference is \(4.4\) (which is \(3.3 + 1.1\)),
- The fifth difference should logically be \(5.5\) (which is \(4.4 + 1.1\)).

5. **Check the Fifth Difference:**
However, we found that the difference between 18 and 13 is \(5\), not \(5.5\). This indicates that \(18\) is inconsistent with the pattern.

6. **Calculate the Correct Value:**
If we had followed the pattern, the term after \(13\) should have been:
\[ 13 + 5.5 = 18.5 \]

7. **Conclusion:**
Therefore, the odd one out in the series is \(18\). The correct number should be \(18.5\).

### Final Answer:
The odd one out is **18**.