The correct answer is D. Individual seller/buyer can influence price in the market.
Perfect competition is a market structure in which there are many buyers and sellers of a homogeneous product, and no one buyer or seller has a significant impact on the market price. The other three options are all characteristics of perfect competition.
A large number of firms means that no one firm has a large share of the market. This prevents any one firm from having too much power to influence the price.
Perfect mobility of factors means that resources can move freely between industries. This means that firms can easily enter or exit the market, and that workers can easily move between jobs.
Price is determined by industry not by individual firm means that the price of a good or service is determined by the interaction of supply and demand in the market, and not by any individual firm.
Individual seller/buyer can influence price in the market means that a single buyer or seller can have a significant impact on the market price. This is not a characteristic of perfect competition.