Select the number from among the given options that can replace the question mark (?) in the following series.

21, 30, 23, 32, 25, ?

21, 30, 23, 32, 25, ?

Odd terms: 21,23,25: These increase by +2.

So, the next odd term will be 25+2=27.

Even terms: 30,32,?: These increase by +2.
So, the next even term will be 32+2=34.

Thus, the sequence becomes:
21, 30, 23, 32, 25, 34.

The missing number is 34.

Thus, correct option (b).