ANS:B - 1

10101000111 This 1's and 0's binary language which can understand by computer.

It's hard to do operations on this binary numbers. To simplify this we use 1's and 2's compliment. Like if we have to subtract to binary number just find the 1's complement of number and add them together instead of subtracting.(adding binary number is simpler than subtracting).

1's compliment of 111000110010 is = 000111001101("0 converted to 1" and "1 converted to 0");

2's compliment of 111000110010 is = 000111001101 + 1 = 000111001110...