Four fruits are given – apple, litchi, guava and orange. Three of these are non-citrus fruits, while one is a citrus fruit. Which of the following fruits is the odd one out in this group?

Introduction / Context:
This classification question is based on basic knowledge of fruits and their categories. In aptitude and reasoning examinations, questions often ask you to identify a fruit that belongs to a different botanical or culinary group from the rest. Here, three fruits are non citrus, while one fruit is clearly a citrus fruit known for its high vitamin C and tangy taste.

Given Data / Assumptions:
The fruits listed are apple, litchi, guava and orange.
You are expected to know which fruits are commonly considered citrus fruits (such as orange, lemon and lime) and which are not.
Three fruits should belong to the non citrus group, and one fruit should be a citrus fruit with characteristic sour taste and juicy segments.
The fruit that differs in this way will be the odd one out.

Concept / Approach:
Citrus fruits belong to the citrus family and include fruits like orange, lemon and grapefruit. They generally have a segmented juicy pulp and a distinctly tangy or sour flavour. Non citrus fruits like apple, litchi and guava do not fall into this botanical group and have different internal structures and taste profiles. Identifying which one among the options is a citrus fruit allows you to choose the odd one out easily.

Step-by-Step Solution:
Step 1: Apple is a non citrus fruit. It has firm flesh, many small seeds in the core and is sweet or slightly tangy, but it is not a member of the citrus family. Step 2: Litchi is also a non citrus fruit. It has a single large seed surrounded by sweet, translucent pulp and does not have the typical citrus segments. Step 3: Guava is another non citrus fruit. While guava is rich in vitamin C, it belongs to a different botanical family and has multiple small seeds embedded in its flesh rather than citrus like segments. Step 4: Orange is a classic citrus fruit. It belongs to the citrus family, has segmented juicy pulp, a distinctly acidic or tangy taste and a characteristic citrus aroma. Step 5: Group the fruits: apple, litchi and guava are non citrus varieties, while orange is a citrus fruit. Step 6: Therefore, orange is different in category and is the odd one out among the four options.

Verification / Alternative check:
Another quick check is to remember which fruits are typically listed when people talk about citrus fruits. Orange is always in that list along with lemon and lime. Apple, litchi and guava are never grouped with citrus fruits, even though some may also be rich in vitamin C. This confirms that the obvious classification difference is citrus versus non citrus, and orange alone belongs to the citrus side.

Why Other Options Are Wrong:
Apple: A non citrus fruit; it shares this category with litchi and guava.
Litchi: Also a non citrus fruit and not the odd one out.
Guava: Non citrus fruit despite its high vitamin C content; it still is grouped with apple and litchi rather than with citrus fruits.

Common Pitfalls:
Some candidates may get confused because guava is also associated with vitamin C, similar to citrus fruits. However, vitamin C content does not alone determine the citrus category. Always rely on the common classification and structural properties like segments and typical citrus flavour. Among the given options, orange is unmistakably the citrus fruit.

Final Answer:
The fruit that belongs to the citrus family and is therefore the odd one out is Orange.