Decimal value of octal digit – UGC NET Question

In positional number systems, single digits from 0 up to base minus one share the same numeric meaning across bases. In octal, digit '5' therefore represents the quantity five, just as it does in decimal. The difference lies in how multi-digit numbers are interpreted, not in the meaning of a standalone digit.

Option A:
Option A, 3, would correspond to the digit '3', not '5'. There is no reason for '5' to map to a smaller value in octal.

Option B:
Option B, 4, is likewise associated with the digit '4'. Octal does not remap the meanings of the basic digits 0 through 7 when they appear alone.

Option C:
Option C is correct because a single octal digit '5' has the same magnitude as decimal 5 when considered in isolation. The positional context only becomes important when digits combine.

Option D:
Option D, 6, would be the value of octal digit '6', not '5'. Changing the meaning like this would break consistency across number systems.