Answer:
C. 30.0 g NaOH and add water until the final solution has a volume of 3.00 L.
Explanation:
Molarity of a substance , is the number of moles present in a liter of solution .
M = n / V
M = molarity
V = volume of solution in liter ,
n = moles of solute ,
from the question ,
M = 0.250M
V = 3.00 L
M = n / V
n = M * v
n = 0.250M * 3.00 L = 0.75 mol
Moles is denoted by given mass divided by the molecular mass ,
Hence ,
n = w / m
n = moles ,
w = given mass ,
m = molecular mass .
From the question ,
n = 0.75 mol NaOH
m = molecular mass of NaOH = 40 g/mol
n = w / m
w = n * m
w = 0.75 mol * 40 g/mol = 30.0 g
Hence , by using 30.0 g of NaOH and dissolving it to make up the volume to 3 L , a solution of 0.250 M can be prepared .
<u>Answer:</u>
<u>For A:</u> The average molecular speed of Ne gas is 553 m/s at the same temperature.
<u>For B:</u> The rate of effusion of
gas is 
<u>Explanation:</u>
<u>For A:</u>
The average molecular speed of the gas is calculated by using the formula:

OR

where, M is the molar mass of gas
Forming an equation for the two gases:
.....(1)
Given values:

Plugging values in equation 1:

Hence, the average molecular speed of Ne gas is 553 m/s at the same temperature.
<u>For B:</u>
Graham's law states that the rate of diffusion of a gas is inversely proportional to the square root of the molar mass of the gas. The equation for this follows:

Where, M is the molar mass of the gas
Forming an equation for the two gases:
.....(2)
Given values:

Plugging values in equation 2:

Hence, the rate of effusion of
gas is 
A colorless, toxic, radioactive gas is called, bioaccumulation.
The identity of a metal that has a mass of 27.0g and a volume of 10.0cm is Aluminium. That is option B.
<h3>What is molar mass?</h3>
Molar mass is defined as the mass in grams of one mole of an element. This is measured in grams/mole of that substance.
The metal that is 27.0 g and a volume of 10.0 cm3 is aluminium because aluminium is 27 times heavier than 1/12th of the mass of carbon-12 atom.
Therefore, the identity of a metal that has a mass of 27.0g and a volume of 10.0cm is Aluminium.
Learn more about molar mass here:
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