Explanation:

- Let's examine the series: 7, 4, 5, 9, 21, 52.5, 160.5.

- First difference: 4 - 7 = -3

- Second difference: 5 - 4 = 1

- Third difference: 9 - 5 = 4

- Fourth difference: 21 - 9 = 12

- Fifth difference: 52.5 - 21 = 31.5

- The pattern isn't consistent.

- Let's investigate each term:

1. 7 is the starting number.

2. The second term, 4, seems incorrect because the expected pattern is not followed here.

3. Each subsequent term should follow some logical pattern.

- Analyzing deeper indicates that 4 doesn't fit well with a consistent multiplication or addition sequence.

- 4 is the incorrect term as it disrupts potential logical sequences.

- Your Answer is Option:5, 4.

ANSWER: Option 5, 4