Answer:
explanation below
Explanation:
Dichlorodiphenyltrichloroethane, also known as DDT is a chemical compound that is found in insecticides. In 1972, the United States Environmental Protection Agency issued an order for the cancellation of requests for the chemical compound because it affects wildlife and pose risks to humans as well.
From the question here, it was noted that the initial concentration was 22ppm 25years ago and so if it takes 7years to decay by half, the actual concentration in present day farmers could be calculated as follows;
25years ago - 22ppm
18years ago - 11ppm
11years ago – 5.5 ppm
4 years ago - 2.75ppm
Since 7yrs = 0.5
Then 4yrs will be [ [4/7] x 0.5] = 0.2857
Then if 0.5 = 2,
Then 0.2857 = [ [ 0.2857/0.5] x 2] = 1.1428
So present year concentration would then be [2.75ppm/1.1428] = 2.406ppm
True but no one know Exactly how many stars there are
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This is a characteristic of a Thermosetting polymer.
Answer:
B. Periods
Explanation:
The horizontal rows in the periodic table are periods.
on the picture below, u can see an example