The octal number system has a base of ______.

The octal number system is a base-8 system, meaning it uses 8 digits: 0, 1, 2, 3, 4, 5, 6, and 7. The base of a number system is the total number of unique digits it uses. Since octal uses 8 digits, its base is 8. Option A (10) is incorrect because 10 is the base of the decimal system, not octal. Option C (16) is incorrect because 16 is the base of the hexadecimal system, which uses digits 0–9 and letters A–F. Option D (4) is incorrect because a base of 4 would only allow digits 0, 1, 2, and 3, which is insufficient for octal digits like 5, 6, and 7. Option E (Question not attempted) is invalid because the question is answerable with basic knowledge of number systems.