Oxygen is an element in the sixth group of the periodic table. This means it contains 6 electrons in its valence shell. Therefore, to complete its octet, it will prefer to gain two electrons rather than to donate 6. This is why its valency is -2. The relatively easy to achieve octet makes Oxygen a reactive element.
An aggregate of cells in an organism that have similar structure and function.
There us a 100 percent chance that her son will have color blindness because the son gets one of the mom's x chromosomes which will have color blindness because both of the mom's x chromosomes carry color blindness, and he only has 1 x chromosome, so he will definitely have color blindness.
Earth's history. In the worst one, 250 million years ago, 96 percent of marine species and 70 percent of land species died off. It took millions of years to recover.
