The chemical formula for water is H2<span>O which means that every </span>molecule<span> of water has 2 </span>atoms<span> of hydrogen (H) and one </span>atom<span> of oxygen (O). Here comes the key part. From the Periodic Table of Elements, one sees that one mole of hydrogen </span>atoms weighs <span>1 gram while one mole of oxygen </span>atoms<span> weighs 16 grams.</span>
Answer:

Step-by-step explanation:
The percentage of the semicircle shaded section is approximately 23,606 %.
The percentage of the area of the semicircle is equal to the ratio of the semicircle area minus the half-cross area to the semicircle area. In other words, we have the following expression:

(1)
Where:
- Area of the half cross, in square centimeters.
- Area of the semicircle, in square centimeters.
- Percentage of the shaded section of the semicircle.
And the percentage of the shaded section is:
![r = \left[1-\frac{4 \cdot (2\,cm)^{2}+4\cdot \left(\frac{1}{2} \right)\cdot (2\,cm)^{2}}{0.5\cdot \pi\cdot (16\,cm^{2}+4\,cm^{2})} \right]\times 100](https://tex.z-dn.net/?f=r%20%3D%20%5Cleft%5B1-%5Cfrac%7B4%20%5Ccdot%20%282%5C%2Ccm%29%5E%7B2%7D%2B4%5Ccdot%20%5Cleft%28%5Cfrac%7B1%7D%7B2%7D%20%5Cright%29%5Ccdot%20%282%5C%2Ccm%29%5E%7B2%7D%7D%7B0.5%5Ccdot%20%5Cpi%5Ccdot%20%2816%5C%2Ccm%5E%7B2%7D%2B4%5C%2Ccm%5E%7B2%7D%29%7D%20%5Cright%5D%5Ctimes%20100)

The percentage of the semicircle shaded section is approximately 23,606 %.
We kindly invite to check this question on percentages: brainly.com/question/15469506