Gold is found in pure state in nature but not the iron because gold is un-reactive metal, so it does not react with other element in normal condition but iron is reactive metal so it reacts with atmospheric oxygen in presence of moist (water) to form oxide.
Explanation:
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Extensive properties, such as mass and volume, depend on the amount of matter being measured. Intensive properties, such as density and color, do not depend on the amount of the substance present. Physical properties can be measured without changing a substance's chemical identity.
Answer:
The correct option is: A. activity; concentration
Explanation:
A reaction rate essay is a laboratory method to determine the activity of an enzyme. It is necessary for determining the enzyme kinetics and inhibition.
Whereas, a colorimetric analysis is a method to determine the concentration of a chemical compound in a solution. Therefore, a colorimetric endpoint assay measures the concentration.
Therefore, Enzyme activity is measured by a reaction rate assay and the concentration is measured by a colorimetric endpoint assay.
Answer:

Explanation:
R = Rydberg constant = 
= Principal quantum number of an energy level = 2
= Principal quantum number of an energy level for the atomic electron transition = 4
Wavelength is given by the Rydberg formula

The wavelength of the light emitted is
.