I think it’s D............
Answer:
A food chain is a representation of what eats what in an ecosystem.
A combination of food chains is termed as a food web.
Example of two food chains in a food web are :
Example No 1:
Plant----- Grasshopper------ Frog---snake--- bacteria
Example No 2:
Plant---- rabbits---- fox---- bacteria
In a food chain, producers are usually plants and algae which are able to make their own food. Consumers feed on the plants. In example no 1, grasshoppers are primary consumers, frogs are secondary consumers, snakes are tertiary consumers.
In example no 2,plants are producers, rabbits are primary consumers and foxed are secondary consumers.
Decomposers are organisms that feed on the dead organisms in a food chain. In both the examples of food chain, bacteria are the decomposers.
The two are potassium and rubidium. Why? Na is an alkali metal. As you go down the metals become more reactive.
Calcium has 20 protons. Why? The atomic # is 20 (the one at the top).
It has 20 neutrons. Why? The atomic mass (the number on the bottom) is ~40, ignoring electron mass. 40- 20 protons = 20 neutrons.
It has 20 electrons.
Why? The # of protons and electrons is the same. Ions aren't on the periodic table.
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Nothing
Explanation:
Mass of the sample = 500g
Decay rate per anum = 11%
Unknown:
Mass of sample remaining after 10yrs = ?
Solution:
This is a simple percentages problem;
The radioactive sample loses 
x 500g of sample per year;
this is a loss of 55g per year;
In 10years time, the sample would have lost 10 x 55g = 550g of element.
Since our sample is not up to 550g, then no amount of sample will remain after 10yrs.
learn more:
Radioactive decay brainly.com/question/10094982
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