In a binary number, which bit is the most significant?

• A. Most significant bit
• B. Least significant bit
• C. The sign bit
• D. A placeholder

Answer: (A)

In binary, each position represents a power of two, and the leftmost position has the highest power. The bit in that leftmost position is the most significant bit because changing it changes the value by the largest amount (for an n-bit number, that bit adds 2^(n-1) when it’s 1). For example, in an 8-bit number, the leftmost bit contributes 128 if it’s 1, which greatly affects the total value, more than any other bit can. The least significant bit is the rightmost one and has the smallest contribution (2^0). The sign bit is used in signed representations to indicate positive or negative values, and while it’s often the leftmost bit in common formats, it isn’t a universal rule for all binary numbers. A placeholder isn’t a standard term for any bit position. So the bit with the greatest weight is the most significant bit.