Answer: Please see answer below
Step-by-step explanation:
Headsets- perfect competition ---- This is because the market structure has many firms selling selling similar products, so there will be competition with the absence of price control by a particular firm.
Smart phones- monopolistic competition ---- This smart phone manufacturers use advertising to differentiate their products because even though the smart phones market here have many firms producing slightly same products , each firm has different products which cannot be perfectly substituted therefore operating in a monopolistic competitive medium
Cellular telephone service - oligopoly --- . In this Cellular telephone service market, there are a few firms that are selling either same or different services and so the few firms influence each other.
Cell phone applications - monopolistic competitions---- This is because many firms are selling different products and therefore decisions on price and the company depend on individual firm which leads monopolistic competition.