B (8 < log2(500) < 9).

28 = 256 and 29 = 512.

If you successively divide by two, starting with 500 and rounding down to the nearest integer where necessary, you get

500
250
125
62
31
15
7
3
1
A total of 8 halving steps are needed to reach 1. That tells you that log2(500) >= 8.

If you successively divide by two, starting with 500 and rounding up to the nearest integer where necessary, you get

500
250
125
63
32
16
8
4
2
1
A total of 9 halving steps are needed to reach 1. That tells you that log2(500) <= 9.

Putting those together, you see that log2(500) must lie between 8 and 9.