Fluorine has an atomic number of 9. Which of the following would you do to a neutral fluorine atom to complete its valence shell?
A) add 1 electron
B) add 2 electrons
C) remove 1 electron
D) Nothing. If fluorine is neutral, it has a complete valance shell.
A
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Excess nutrients in the aquatic environment can cause an initial population surge of primary producers, but eventually results in a collapse of the ecosystem. Which of the following answer choices is not a direct reflection of this statement?
A. Habitats have a particular carrying capacity. B. All trophic levels can be interdependent. C. Communities are shaped by the physical environment. D. Animals interact with their physical environment.
Conducting tubes of phloem consist of stacks of ____
a. dead sieve elements b. living sieve elements c. dead vessel elements d. living vessel elements e. dead companion cells
Which of the following would NOT be evidence that mitochondria were once prokaryotic?
a. similarities of mitochondrial ribosomes and bacterial ribosomes a. similarities of mitochondrial ribosomes and bacterial ribosomes b. negative effects of antibiotics on mitochondria c. DNA similarities of mitochondria and free-living bacteria d. the presence of a circular chromosome e. presence of a nucleus within mitochondria
Keystone species are:
A) might be of any number, anywhere on the food chain. B) always at the top of the food chain. C) always the most numerous. D) never at the top of the food chain.