When a pure public good is non-excludable and is provided only through voluntary private contributions, the outcome is typically:

When a good is non-excludable, no one can be prevented from consuming it, whether or not he pays for it. Each individual therefore finds it beneficial to understate his true valuation and let others bear the cost. Each person weighs only his own benefit against the cost of contributing, so total contributions stop short of the point where the sum of marginal benefits equals marginal cost. In the simplest two-choice game, contributing nothing is a dominant strategy; with continuous contributions, high-demand individuals may give something, but the total still falls short of the efficient (Samuelson) level. Taking the options one by one: Option (A): a Lindahl equilibrium, with personalised prices equal to marginal benefits, would be Pareto optimal. But it works only if individuals reveal their true preferences, and non-excludability gives them every incentive not to. Voluntary private provision therefore does not reach it. Option (B): saddle-path stability is a concept of dynamic macroeconomic models and has no relevance here. Option (C): competitive pricing breaks down because a price cannot be charged for a good from which nobody can be excluded. Option (E): a market price cannot reveal true marginal valuations here, because people who cannot be excluded have no reason to pay in line with their valuations. Hence the correct option is (D).