<u>Answer:</u>
A measurement standard is defined as 'the exact quantity people agree to use for comparison'.
<u>Explanation:</u>
For the same type of quantity, there is a unit of measurement which is defined and adopted either conventionally or by law which is used as standard for measurement of that quantity.
This measurement standard is defined as 'the exact quantity people agree to use for comparison'.
For example, for length the standard unit of measurement is 'meter'.
The purpose of nucleophilic substitution reactions of alkyl halides experiment is to demonstrate in the laboratory setting Nucleophilic substitution reactions of alkyl halides.
In this it is been aimed to observe nucleophilic substitution reactions, SN1 and SN2 will by the addition of a solvent to mixtures of alkyl halides. In order to make this experiment effective a standard procedure is being used and noted observations while each reaction occurred.
Nucleophilic substitution reactions are an important class of reactions that allow the interconversion of functional groups. For alcohols, the range of substitution reactions possible can be increased by utilizing the tosylates (R-OTs), an alternative method of converting the -OH to a better leaving group.
To learn more about nucleophilic substitution reactions
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Answer:
A) receding from the earth
B) 
Explanation:
- A) receding from the earth
The wavelength went from 434.1nm to 438.6nm, there was an increase in wavelength (also knowecn as redshift due to the doppler efft), this increase is due to the fact that the source that emits the radiation (the distant galaxy) is moving away and therefore the light waves it emits are "stretched", causing us to see a wavelength greater than the original.
- B)

to calculate the relative speed we use the following formula:

where
is the speed of light:
is the wavelength emited by the source, and
is the wavelength measured on earth.
we substitute all the values and do the calculations:

the relative speed is: 