A) 60b or 450D

B) 45b or 300D

C) 30b or 200D

D) 15b or 100D

As per clause 25.1.1 of IS 456-2000, the unsupported length (l) of a column whose one end is unrestrained in any given plane shall not exceed the smaller of 30b or 200D, where b is the width and D is the depth of the column cross-section.

Therefore, option C is the correct answer.