Answer:
In the base-two system, the number after 1001₂ (which is equivalent to 9 in decimal) would be 1010₂.
Explanation:
To find the next whole number in binary after 1001₂, you simply increment the rightmost digit (bit). So, changing the 1 to 0 and carrying over the increment to the next bit results in 1010₂, which is equal to 10 in decimal.