Which of the following is having largest size?

The size of an antibody (a protein molecule) is approximately $10$ nm.

The size of a typical virus ranges from $20$ nm to $300$ nm.

The size of a typical bacterium ranges from $0.5\mu$ m to $5\mu$ m (500$nm to 5000$ nm).

The size of a cancer cell (a eukaryotic human cell) typically ranges from $10\mu$ m to $30\mu$ m (10000$nm to 30000$ nm).

Comparing the sizes, the cancer cell is the largest among the given options.

Answer: Cancer cell