The octal number system consists of the following symbols:

Concept — A positional number system of base (radix) b uses exactly b distinct digit symbols, running from 0 up to b − 1. The base therefore fixes both how many symbols the system has and which one is largest, and every digit contributes its face value times a power of b.

Application — Octal is the base-8 system, so it uses exactly eight symbols: 0, 1, 2, 3, 4, 5, 6 and 7. The largest permitted symbol is b − 1 = 8 − 1 = 7, which is why the marks 8 and 9 can never appear inside an octal numeral — the quantity eight is already written as 108. Reading the octal numeral 7258 shows the place values at work:

1. Write each place value as a power of the base: 82, 81, 80.

2. Multiply every digit by its place value: 7 × 82 = 448, 2 × 81 = 16, 5 × 80 = 5.

3. Add the products: 448 + 16 + 5 = 469, so 7258 = 46910.

Cross-check — counting the symbols in each common base makes the pattern explicit:

Only the eight-symbol set 0 – 7 fits base 8, so the octal symbol set is 0 – 7. The ten-symbol set 0 – 9 belongs to decimal, and the sixteen-symbol set 0 – 9, A – F belongs to hexadecimal, where A to F stand for the values 10 to 15. Since one of the listed sets does match octal, the answer "None of the above" does not apply.