The correct answer is option 'D', 3.125%. Let's break down the explanation step by step.

Half-life:
The half-life of a radioactive substance is the time it takes for half of the radioactive atoms in a sample to decay. It is a characteristic property of each radioactive element.

After one half-life:
After one half-life, half of the original radioactive atoms have decayed, and the remaining half is still radioactive.

After two half-lives:
After two half-lives, half of the remaining radioactive atoms from the first half-life have decayed. This means that 3/4 (or 75%) of the original radioactive atoms have decayed, and 1/4 (or 25%) are still radioactive.

After three half-lives:
After three half-lives, half of the remaining radioactive atoms from the second half-life have decayed. This means that 7/8 (or 87.5%) of the original radioactive atoms have decayed, and 1/8 (or 12.5%) are still radioactive.

After four half-lives:
After four half-lives, half of the remaining radioactive atoms from the third half-life have decayed. This means that 15/16 (or 93.75%) of the original radioactive atoms have decayed, and 1/16 (or 6.25%) are still radioactive.

After five half-lives:
After five half-lives, half of the remaining radioactive atoms from the fourth half-life have decayed. This means that 31/32 (or 96.875%) of the original radioactive atoms have decayed, and 1/32 (or 3.125%) are still radioactive.

Therefore, after five half-lives, only 3.125% of the original radioactive atoms are left.

To summarize:
- After one half-life: 50% of the original radioactive atoms are left.
- After two half-lives: 25% of the original radioactive atoms are left.
- After three half-lives: 12.5% of the original radioactive atoms are left.
- After four half-lives: 6.25% of the original radioactive atoms are left.
- After five half-lives: 3.125% of the original radioactive atoms are left.