What is the binary number for IP address 172.16.5.20?

ip add consist of four octets separated by dot. each octet consist of 8 bits. see below.

xxxxxxxx.xxxxxxxx.xxxxxxxx.xxxxxxxx;

each bit per octet has an equivalent decimal value, the first bit, the right most bit, the equivalent value of that is 1 then the next bit is 2 then 4, 8, 16, 32, 64 and 128. as you notice you just multiply by 2 starting from the first bit. 2 is our multiplier because binary is using the power of 2. if all the eight bits are 1 then the decimal equivalent of that is 255 just simply add all the decimal equivalent of each bit and you will get 255. so if you will convert 172 into binary that will be 10101100. if you add those decimal equivalent of those with 1 you will get 172. just always remember the decimal equivalent of each bit in an octet.

1 1 1 1 1 1 1 1

128 64 32 16 8 4 2 1

to complete your question, see below answer.

172.16.5.20 = 10101100.00010000.00000101.00010100