How many bits are required to count upto decimal 1 million?

One bit can be one or zero: 2 states. Two bits can count four states. Each additional bit doubles the possible count. A computer operates with eight bits at a time, called a byte, and that allows 256 different codes. If you are going to work with a computer you should memorize all the numbers up to whatever you work with often.

bits - states
1 - 2
2 - 4
3 - 8
4 - 16
5 - 32
6 - 64
7 - 128 <-- This is enough to encode all printable characters in the ASCII standard.
8 - 256

16 - 65536
32 - 4,294,967,296 <-- In computer memory or file sizes, this is called "4 gigabytes".
and so on.