Four crop names are given – rice, wheat, barley and mustard. Three of these are cereal grains, while one belongs to a different category. Which of the following is the odd one out?

Introduction / Context:
This is a simple general knowledge and classification question related to agriculture. You are given four crop names and asked to pick the one that does not belong to the same category as the others. Such questions frequently test your familiarity with basic crop classification, especially the distinction between cereals and oilseeds.

Given Data / Assumptions:
The options are rice, wheat, barley and mustard.
You are expected to know which of these crops are cereal grains and which belong to other agricultural categories.
Three of the crops are staple cereal grains, usually grown for their edible seeds, while one is mainly grown as an oilseed and a spice crop.
The answer is the crop that is not a cereal grain.

Concept / Approach:
Cereal crops are grasses cultivated for their edible grains or seeds. In many parts of the world, cereals are the main component of staple food. Rice, wheat and barley are classic cereal crops. Mustard, however, belongs to the mustard family and is primarily grown for its seeds, which are used to produce mustard oil and to make condiments. Recognising this difference in agricultural category helps you correctly identify the odd one out.

Step-by-Step Solution:
Step 1: Identify rice. Rice is a major cereal grain grown in many regions, especially in Asia. It belongs to the grass family and its grains are eaten as a staple food. Step 2: Identify wheat. Wheat is another very important cereal grain from the grass family. Its grains are used to make flour, bread, chapati, pasta and many other food products. Step 3: Identify barley. Barley is also a cereal crop, belonging to the grass family, used for animal feed, malt production and various foods. Step 4: Now examine mustard. Mustard is not a cereal grain. It is an oilseed crop from the mustard family, and its seeds are used to produce mustard oil and to spice foods. Step 5: Categorise the crops: rice, wheat and barley belong to the cereal group, while mustard belongs to the oilseed and spice category. Step 6: Therefore, mustard is different from the others and is the odd one out.

Verification / Alternative check:
Another way to think about it is to recall what part of the plant is mainly used and in what way. For rice, wheat and barley, the main usable part is the grain, which is consumed directly as food. For mustard, the seeds are pressed for oil or used as a spice, and it is not a staple grain. This confirms that mustard does not share the primary cereal grain category with the other three crops.

Why Other Options Are Wrong:
Rice: A major cereal crop, so it clearly belongs to the group of cereals.
Wheat: Another staple cereal grain, similar in nature to rice and barley.
Barley: Also a cereal crop used for food and malt, so it is not the odd one out.

Common Pitfalls:
Sometimes candidates misclassify barley because it is less commonly eaten directly as a staple compared to rice or wheat, but it is still a cereal. Remember that cereals are defined botanically as grasses grown for edible grains, and barley fits this definition. Mustard stands out clearly as an oilseed crop used mainly for oil and spice, so that should be your focus.

Final Answer:
The only crop among the options that is not a cereal grain is Mustard.