Which type of agreement allows a seller to give a buyer the right to purchase an interest in property for a specified time?

The correct answer is an option agreement because it is specifically designed to grant the buyer the right, but not the obligation, to purchase a property at a predetermined price within a specified timeframe. This type of agreement provides the buyer with the flexibility to formalize the purchase at a later date, which is advantageous in managing both investment risks and opportunities.

In contrast, a standard purchase agreement typically involves a binding commitment from both parties to complete the sale immediately upon agreement, which does not allow for a delayed decision like an option agreement does. An installment sale agreement facilitates the sale of property through a series of payments over time but does not inherently provide an option to purchase within a certain period—it is more about the structure of payment for an already agreed-upon sale. A lease agreement generally involves renting property for a period without implying any purchase option, as it maintains the landlord-tenant relationship rather than a buyer-seller relationship.