Hello

The first fundamental theoram of welfare economy states that  a market will tend towards a competitive equilibrium that is weakly Pareto optimal when the market maintains the following two attributes

• Complete market with no transaction costs and Therefore each sector  also having perfect information.

•Price taking behavior with no monopolists and easy entry and exit from a market.

The perfect information is reffered to as no hidden information. With perfect information in a market , all consumers and producers have perfect and instantaneous knowledge of all market prices, their own  utility and own cost functions.