Which of the followings statements is/are true about private goods?

I. Rivalrous in consumption

II. Non-excludability

III. Negative marginal cost

The correct option is I only.

To understand why this is the correct answer, let us break down the economic properties that define a private good:

1. Rivalry in Consumption (Statement I):
A good is rivalrous if one person's consumption of it reduces the quantity or quality available for others to consume. Private goods (such as an apple, a car, or a piece of clothing) are fully rivalrous because if one person buys and uses the item, no one else can use that exact same unit. Therefore, Statement I is true.

2. Excludability (Statement II):
Private goods are excludable, meaning it is possible to prevent individuals who have not paid for the good from consuming or using it (for example, through price tags or legal ownership). Non-excludability is a feature of public goods or common resources, not private goods. Therefore, Statement II is false.

3. Marginal Cost (Statement III):
Producing an additional unit of a private good incurs a positive marginal cost, representing the additional cost of raw materials, labor, and resources needed. Marginal cost is typically positive, not negative. Therefore, Statement III is false.

Conclusion:
Since only Statement I is true regarding private goods, the correct option is I only.