The pollen diameter of chrysanthemum, peach and plum is about 50um, 30um and 20um respectively. Please use scientific counting method to show how many meters each of them is equivalent to?

The pollen diameter of chrysanthemum, peach and plum is about 50um, 30um and 20um respectively. Please use scientific counting method to show how many meters each of them is equivalent to?

5 × 10 negative quintic meter
3 × 10 negative quintic meter
2 × 10 negative quintic meter