A number series is given with one term missing. Choose the correct alternative from the given options that will complete the series: -4, ?, 1, 3.5, 6, 8.5.

Introduction / Context:
This question is a classic arithmetic number series problem from verbal reasoning. The task is to identify the numerical pattern that generates the sequence and then use that pattern to find the missing term. Such questions help evaluate understanding of arithmetic progressions and the ability to work with fractional increments.

Given Data / Assumptions:
Given series: -4, ?, 1, 3.5, 6, 8.5.Exactly one term, the second, is missing.We assume a simple and consistent pattern applies across all consecutive terms.

Concept / Approach:
The natural first step is to look at the differences between consecutive known terms. If these differences are constant, the sequence is an arithmetic progression. If they follow their own pattern, we then analyze that secondary pattern. In this case, the presence of decimal numbers like 3.5 and 8.5 suggests a fixed fractional increment, which strongly hints at an arithmetic progression with a non-integer common difference.

Step-by-Step Solution:
Step 1: Compute the difference between 1 and 3.5: 3.5 - 1 = 2.5.Step 2: Compute the difference between 3.5 and 6: 6 - 3.5 = 2.5.Step 3: Compute the difference between 6 and 8.5: 8.5 - 6 = 2.5.Step 4: The common difference for the known part of the series is therefore 2.5.Step 5: Let the missing term be x. Since 1 is the next term after x, we must have 1 - x = 2.5, so x = 1 - 2.5 = -1.5.Step 6: Check the difference from -4 to x: -1.5 - (-4) = -1.5 + 4 = 2.5, which matches the established common difference.

Verification / Alternative check:
Write the complete series with the candidate term: -4, -1.5, 1, 3.5, 6, 8.5. Now verify every step: -4 + 2.5 = -1.5, -1.5 + 2.5 = 1, 1 + 2.5 = 3.5, 3.5 + 2.5 = 6, and 6 + 2.5 = 8.5. The progression is perfectly consistent, confirming that the pattern is an arithmetic series with common difference 2.5 and that x = -1.5 is correct.

Why Other Options Are Wrong:
Option 2 gives the series -4, 2, 1, which breaks the constant difference rule because 1 - 2 = -1, not 2.5.Option 1.5 leads to 1 - 1.5 = -0.5, which again does not match the difference 2.5 observed later in the series.Option -2 produces a difference of 2 between -4 and -2, which is inconsistent with the 2.5 difference that appears between the later terms.

Common Pitfalls:
Students sometimes try to fit different differences at different parts of the series, which usually makes the pattern needlessly complicated. Another common mistake is ignoring the fractional part and assuming only whole number steps. In competitive exams, the simplest consistent pattern, such as a fixed difference, is almost always intended unless the question explicitly suggests otherwise.

Final Answer:
The missing term that completes the arithmetic series is -1.5.