C. crop rotation
Explanation:
Crop rotation is a farming practice that is commonly used to maintain a healthy soil.
This practices helps to conserve and appropriate a soil for the best use.
During crop rotation, different crop species are planted during a growing season. The patterns are designed to cultivate both crops that replenish and deplete the nutrients in soil.
Through this the fertility of the soil is sustained all year round.
This helps to avoid the use of pesticides on crops.
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Answer: A pattern of same atomic orbitals can be seen about elements in the same period with respect to electron structures.
Explanation:
The horizontal rows in a period table are called periods.
Elements present in the same period will have same atomic orbitals.
For example, electronic distribution of Na is 2, 8, 1 and it is a third period element.
Similarly, electronic distribution of Cl is 2, 8, 7 and it is also a third period element.
Hence, both Na and Cl will have K, L, M shells, that is, they have three atomic orbitals.
Thus, we can conclude that a pattern of same atomic orbitals can be seen about elements in the same period with respect to electron structures.
Answer:
Zinc metal might be mixed with the copper.
Explanation:
Density is defined as mass of the substance present in the unit volume of the substance.

Density of pure copper = d = 8.94 g/mL = 

Mass of the copper penny = M = 2.49 g
Volume of the copper penny = V = 
Density of the copper penny = d

Density of pure copper > Density of zinc > Density of penny

The metal mixed with copper is zinc to make a penny . This is so because all the other metal given have higher value of density which will increase the density of the copper penny if they were present.
But here the density of the copper penny is smaller than density of pure copper which means that less denser metal than copper is also added in the penny.
They can be separated by both means as they are only mixtures. (Two or more substances mixed together, and can be separated.)