ANS:B - 100011₂

In binary 1 is written as 001 and 2 is 010, three is 011, 4 is 100, 5 is 101, 6 is 110 and seven is 111 eight is 1000 nine is 1001 and ten is 1010 accordingly 20 is 10100 and 30 is 11110 plus five 101 total would be 10001.

The concept is 1+1=0 and carry forward 1, further if we multiply 7*5=35 it written in binary as 100011 is.