Which of the following is least risky from the buyer’s viewpoint?

Explanation

Payment (the implication here is 'in full') 60 days after delivery allows the buying organisation time to check the goods carefully, and possibly even use them in that time.

All of the other options would require the buyer to part with money prior to holding the goods, thus exposing that sum to risk. The least risky from the buyer's viewpoint is therefore after 60 days.

Particularly hazardous would be payment at time of order.