C Bacteria evolve and become resistant to antibiotics.
Explanation:
Bacteria are small micro-organisms found in nature. They are useful to all life and the same time can be harmful.
Bacteria can evolve and become resistant to antibiotics thereby causing serious health problems.
- Bacteria in living cells can develop resistant strains which prevents antibiotics from acting on them.
- With the passage of time, the bacteria can change their structure into that of a more resistant strain.
- This can prevent antibiotics from acting on them and by so inflict serious damage to life.
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Answer:
82.1
Explanation:
Isotopes of the same element are atoms of the same element (so, having same number of protons) having a different number of neutrons (and so, a different atomic mass).
In this problem, this element has 3 different isotopes, with atomic mass (in atomic mass units, a.m.u.) and relative abundance listed below:
1) 78.9 12.6%
2) 80.9 13.9%
3) 82.9 73.5%
In order to calculate the relative atomic mass unit of this element, we have to calculate the weighed average of the relative atomic mass of each isotope.
This means that we can calculate it as the sum of each atomic mass unit multiplied by the relative frequency:
where 
is the atomic mass of each isotope and 
the relative frequency. Therefore, we find:
Answer:
An electric force is exerted between any two charged objects. Objects with the same charge, both positive and both negative, will repel each other, and objects with opposite charges, one positive and one negative, will attract each other.
Explanation:
