UGC NET Questions (Paper – 1)

The standard rule for forming the 2's complement (negative) of a binary number is to first take its 1's complement by inverting all bits and then add 1. This process yields a representation that has desirable arithmetic properties, such as allowing addition to handle subtraction implicitly. Therefore, after the 1's complement, we add 1.

Option A:
Option A, subtract 1, would not produce the correct 2's complement. Subtracting 1 after inversion would generate a different pattern that does not correspond to the intended negative.

Option B:
Option B, add 2, would overshoot the value needed for 2's complement, leading to an incorrect representation except in trivial cases.

Option C:
Option C is correct because inverting the bits and adding 1 creates a pattern that when added to the original number produces zero with a carry, modeling negation. This is the basis of 2's complement arithmetic in computers.

Option D:
Option D, shift right, is related to division by 2 or logical shifts but has nothing to do with forming the negative of a number.