The series follows an arithmetic progression with a common difference of 0.5 (or 1/2). Starting from 0.5, the terms are 1.0, 1.5, and 2.0. Adding 0.5 to 2.0 yields 2.5. Option 90010 is correct because 2.5 fits the sequence before 3.0. Other options like 3 or 1/2 do not maintain the constant increment.