7, 26, 65, 124, 215, 342

Options

A. 7
B. 26
C. 65
D. 124

Explanation

To solve the series: 7, 26, 65, 124, 215, 342, we need to identify the pattern in the numbers.

### Step-by-Step Solution:

1. **Identify the Pattern**:
We can observe that each number in the series seems to be related to the cubes of natural numbers, minus one.

2. **Calculate the Cubes**:
Let's calculate the cubes of the first few natural numbers:
- \(2^3 = 8\)
- \(3^3 = 27\)
- \(4^3 = 64\)
- \(5^3 = 125\)
- \(6^3 = 216\)
- \(7^3 = 343\)

3. **Subtract One from Each Cube**:
Now, we subtract 1 from each of these cubes:
- \(2^3 - 1 = 8 - 1 = 7\)
- \(3^3 - 1 = 27 - 1 = 26\)
- \(4^3 - 1 = 64 - 1 = 63\)
- \(5^3 - 1 = 125 - 1 = 124\)
- \(6^3 - 1 = 216 - 1 = 215\)
- \(7^3 - 1 = 343 - 1 = 342\)

4. **Compare with the Given Series**:
Now, let's compare the results with the given series:
- 7 (matches)
- 26 (matches)
- 65 (does not match, should be 63)
- 124 (matches)
- 215 (matches)
- 342 (matches)

5. **Identify the Wrong Number**:
From our comparison, we see that the number 65 does not fit the pattern. It should be 63 instead.

### Conclusion:
The wrong number in the series is **65**.