By 1650, the indigenous population of the americas and the caribbean had been reduced to about
24 million.
8 million.
800,000.
50-60 million.

At the time of the arrival of Europeans, the indigenous population was estimated to be just below 40 million people. After the contact with European diseases it is said to be significantly reduced and estimates suggest that in 1650 this population could be around 8-9 million people. (this is just an estimate, but it's the best from all the offered answers).