Find the odd one out from the given alternatives:

Correct — C.
Rule: three options are market structures named by how many firms sell.

Monopoly: one seller. Duopoly: two. Oligopoly: a few.
Barter is not a market structure: it is swapping goods for goods, with no money.

The odd one out is Barter → option (c).

Why the others are wrong

• (a)
  Monopoly — Monopoly is a market with a single seller. It belongs with duopoly and oligopoly, which name markets by the number of sellers.
• (b)
  Oligopoly — Oligopoly is a market with a few sellers. Like monopoly and duopoly, it describes a market structure, so it sits inside the group.
• (d)
  Duopoly — Duopoly is a market with exactly two sellers, the simplest case of oligopoly. It fits the seller-count group, so it is not the odd one.

An odd-one-out item asks for the shared category of three options. Here the three -poly words name market structures by the number of sellers: mono (one), duo (two), oligo (a few). The ending comes from the Greek word for selling.

Barter names a way of exchanging, trading goods directly for goods, not a count of sellers. That puts it outside the group.

Key facts

• Monopoly: one seller. Duopoly: two sellers. Oligopoly: a few sellers.
• A duopoly is the simplest form of oligopoly.
• Barter is the direct exchange of goods for goods, without money.

Common traps

• Picking Duopoly because it is the least familiar word, though it is a market structure like the others
• Grouping barter with the rest because all four are about trade

No directly related past PYQ was found.