1. **State the problem:** Simplify the expression $$100^{-\frac{1}{2}}$$ step-by-step. 2. **Recall the rule:** For any positive number $a$ and rational exponent $m/n$, $$a^{\frac{m}{n}} = \sqrt[n]{a^m}$$ and a negative exponent means reciprocal: $$a^{-x} = \frac{1}{a^x}$$. 3. **Apply the negative exponent rule:** $$100^{-\frac{1}{2}} = \frac{1}{100^{\frac{1}{2}}}$$ This corresponds to the placeholder 2A. 4. **Rewrite the fractional exponent as a root:** $$100^{\frac{1}{2}} = \sqrt{100}$$ This corresponds to 2B. 5. **Evaluate the square root:** $$\sqrt{100} = 10$$ This corresponds to 2C. 6. **Substitute back:** $$\frac{1}{100^{\frac{1}{2}}} = \frac{1}{10}$$ This corresponds to 2E. 7. **Summary of the sequence:** $$100^{-\frac{1}{2}} = \frac{1}{100^{\frac{1}{2}}} = \frac{1}{\sqrt{100}} = \frac{1}{10}$$ **Final answer:** $$\boxed{\frac{1}{10}}$$